diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 7e09bb3abe0..a5a107cf861 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -177,6 +177,7 @@ if (current_os == "win") {
   is_mac = false
   is_nacl = false
   is_posix = false
+  is_watchos = false
   is_win = true
 } else if (current_os == "mac") {
   is_android = false
@@ -187,6 +188,7 @@ if (current_os == "win") {
   is_mac = true
   is_nacl = false
   is_posix = true
+  is_watchos = false
   is_win = false
 } else if (current_os == "android") {
   is_android = true
@@ -197,6 +199,7 @@ if (current_os == "win") {
   is_mac = false
   is_nacl = false
   is_posix = true
+  is_watchos = false
   is_win = false
 } else if (current_os == "linux") {
   is_android = false
@@ -207,6 +210,7 @@ if (current_os == "win") {
   is_mac = false
   is_nacl = false
   is_posix = true
+  is_watchos = false
   is_win = false
 } else if (current_os == "fuchsia") {
   is_android = false
@@ -217,6 +221,7 @@ if (current_os == "win") {
   is_mac = false
   is_nacl = false
   is_posix = true
+  is_watchos = false
   is_win = false
 } else if (current_os == "ios") {
   is_android = false
@@ -227,6 +232,23 @@ if (current_os == "win") {
   is_mac = false
   is_nacl = false
   is_posix = true
+  is_watchos = false
+  is_win = false
+} else if (current_os == "watchos") {
+  is_android = false
+  is_chromeos = false
+  is_fuchsia = false
+
+  # watchOS and iOS are similar enough, so almost all codepaths in
+  # BUILD files are the same for watchOS and iOS. Additionally,
+  # BUILD.gn zlib file doesn't support `is_watchos`, but works fine
+  # with `is_ios`.
+  is_ios = true
+  is_linux = false
+  is_mac = false
+  is_nacl = false
+  is_posix = true
+  is_watchos = true
   is_win = false
 }
 
@@ -445,17 +467,19 @@ if (is_win) {
   host_toolchain = "//build/toolchain/mac:clang_$host_cpu"
   set_default_toolchain("//build/toolchain/mac:clang_$current_cpu")
 } else if (is_ios) {
-  import("//build/config/ios/ios_sdk.gni")  # For use_ios_simulator
+  import("//build/config/ios/ios_sdk.gni")  # For use_simulator
   host_toolchain = "//build/toolchain/mac:clang_$host_cpu"
-  if (use_ios_simulator) {
-    if (target_cpu == "arm64") {
-      set_default_toolchain("//build/toolchain/mac:ios_clang_arm64_sim")
-    } else {
-      set_default_toolchain("//build/toolchain/mac:ios_clang_x64_sim")
-    }
+  toolchain_target = "clang"
+  if (is_watchos) {
+    toolchain_target = "watchos_$toolchain_target"
   } else {
-    set_default_toolchain("//build/toolchain/mac:ios_clang_arm64")
+    toolchain_target = "ios_$toolchain_target"
   }
+  toolchain_target = "${toolchain_target}_$target_cpu"
+  if (use_simulator) {
+    toolchain_target = "${toolchain_target}_sim"
+  }
+  set_default_toolchain("//build/toolchain/mac:$toolchain_target")
 } else if (is_fuchsia) {
   assert(host_cpu == "x64")
   if (host_os == "linux") {
@@ -554,7 +578,8 @@ if (!is_shared_library) {
 
       output_prefix = "lib"
       if (!defined(output_extension)) {
-        if (current_os == "mac" || current_os == "ios") {
+        if (current_os == "mac" || current_os == "ios" ||
+            current_os == "watchos") {
           output_extension = "dylib"
         } else if (current_os == "win") {
           output_extension = "dll"
diff --git a/build/config/ios/ios_sdk.gni b/build/config/ios/ios_sdk.gni
index 4ee46a366e9..25eabedd514 100644
--- a/build/config/ios/ios_sdk.gni
+++ b/build/config/ios/ios_sdk.gni
@@ -6,28 +6,41 @@ import("//build/toolchain/rbe.gni")
 
 declare_args() {
   # SDK path to use. When empty this will use the default SDK based on the
-  # value of use_ios_simulator.
+  # value of use_simulator.
   ios_sdk_path = ""
 
   # Set to true when targeting a simulator build on iOS. False means that the
   # target is for running on the device. The default value is to use the
   # Simulator except when targeting GYP's Xcode builds (for compat with the
   # existing GYP build).
-  use_ios_simulator = false
+  use_simulator = false
 
   # Minimum supported version of the iOS SDK.
   ios_sdk_min = "12.0"
 
+  # Minimum supported version of the watchOS SDK.
+  watchos_sdk_min = "11.0"
+
   # The path to the iOS device SDK.
   ios_device_sdk_path = ""
 
   # The path to the iOS simulator SDK.
   ios_simulator_sdk_path = ""
 
+  # The path to the watchOS device SDK.
+  watchos_device_sdk_path = ""
+
+  # The path to the watchOS simulator SDK.
+  watchos_simulator_sdk_path = ""
+
   ios_enable_relative_sdk_path = use_rbe
 }
 
 if (ios_sdk_path == "") {
+  if (is_watchos) {
+    ios_sdk_min = watchos_sdk_min
+  }
+
   _find_sdk_args = [
     "--print_sdk_path",
     ios_sdk_min,
@@ -42,25 +55,44 @@ if (ios_sdk_path == "") {
     ]
   }
 
-  if (use_ios_simulator && ios_simulator_sdk_path == "") {
-    _find_sdk_args += [ "--platform=iphone_simulator" ]
-    _find_sdk_result =
-        exec_script("//build/mac/find_sdk.py", _find_sdk_args, "list lines")
-    ios_simulator_sdk_path = _find_sdk_result[0]
+  platform = "iphone"
+  if (is_watchos) {
+    platform = "watch"
+  }
+  if (use_simulator) {
+    platform = "${platform}_simulator"
   }
 
-  if (!use_ios_simulator && ios_device_sdk_path == "") {
-    _find_sdk_args += [ "--platform=iphone" ]
-    _find_sdk_result =
-        exec_script("//build/mac/find_sdk.py", _find_sdk_args, "list lines")
-    ios_device_sdk_path = _find_sdk_result[0]
-  }
+  _find_sdk_args += [ "--platform=$platform" ]
+  _find_sdk_result =
+      exec_script("//build/mac/find_sdk.py", _find_sdk_args, "list lines")
+  platform_sdk_path = _find_sdk_result[0]
 
-  if (use_ios_simulator) {
-    assert(ios_simulator_sdk_path != "")
-    ios_sdk_path = ios_simulator_sdk_path
-  } else {
-    assert(ios_device_sdk_path != "")
-    ios_sdk_path = ios_device_sdk_path
+  if (use_simulator && is_watchos) {
+    # watchos_simulator
+    if (watchos_simulator_sdk_path != "") {
+      platform_sdk_path = watchos_simulator_sdk_path
+    }
+    ios_sdk_path = platform_sdk_path
+    ios_sdk_min = watchos_sdk_min
+  } else if (!use_simulator && is_watchos) {
+    # watchos
+    if (watchos_device_sdk_path != "") {
+      platform_sdk_path = watchos_device_sdk_path
+    }
+    ios_sdk_path = platform_sdk_path
+    ios_sdk_min = watchos_sdk_min
+  } else if (use_simulator && !is_watchos) {
+    # ios_simulator
+    if (ios_simulator_sdk_path != "") {
+      platform_sdk_path = ios_simulator_sdk_path
+    }
+    ios_sdk_path = platform_sdk_path
+  } else if (!use_simulator && !is_watchos) {
+    # ios
+    if (ios_device_sdk_path != "") {
+      platform_sdk_path = ios_device_sdk_path
+    }
+    ios_sdk_path = platform_sdk_path
   }
 }
diff --git a/build/toolchain/mac/BUILD.gn b/build/toolchain/mac/BUILD.gn
index 24f4755f51f..88ef256e37c 100644
--- a/build/toolchain/mac/BUILD.gn
+++ b/build/toolchain/mac/BUILD.gn
@@ -78,6 +78,55 @@ mac_toolchain_suite("ios_clang_x64_sim") {
       "-isysroot $ios_sdk_path -mios-simulator-version-min=$ios_sdk_min"
 }
 
+if (is_watchos) {
+  # Toolchain used for watchOS device targets.
+  mac_toolchain_suite("watchos_clang_arm64") {
+    toolchain_cpu = "arm64"
+    toolchain_os = "watchos"
+    prefix = rebased_clang_dir
+    cc = "${compiler_prefix}${prefix}/clang"
+    cxx = "${compiler_prefix}${prefix}/clang++"
+    if (use_rbe) {
+      cc = "${cc} --target=arm64-apple-darwin"
+      cxx = "${cxx} --target=arm64-apple-darwin"
+    }
+    asm = "${assembler_prefix}${prefix}/clang"
+    ar = "${prefix}/llvm-ar"
+    ld = "${link_prefix}${prefix}/clang++"
+    strip = "${prefix}/llvm-strip"
+    nm = "${prefix}/llvm-nm"
+    is_clang = true
+    if (ios_enable_relative_sdk_path) {
+      ios_sdk_path = rebase_path(ios_sdk_path, root_build_dir)
+    }
+    sysroot_flags = "-isysroot $ios_sdk_path -mwatchos-version-min=$ios_sdk_min"
+  }
+
+  # Toolchain used for watchOS simulator targets (arm64).
+  mac_toolchain_suite("watchos_clang_arm64_sim") {
+    toolchain_cpu = "arm64"
+    toolchain_os = "watchos"
+    prefix = rebased_clang_dir
+    cc = "${compiler_prefix}${prefix}/clang"
+    cxx = "${compiler_prefix}${prefix}/clang++"
+    if (use_rbe) {
+      cc = "${cc} --target=arm64-apple-darwin"
+      cxx = "${cxx} --target=arm64-apple-darwin"
+    }
+    asm = "${assembler_prefix}${prefix}/clang"
+    ar = "${prefix}/llvm-ar"
+    ld = "${link_prefix}${prefix}/clang++"
+    strip = "${prefix}/llvm-strip"
+    nm = "${prefix}/llvm-nm"
+    is_clang = true
+    if (ios_enable_relative_sdk_path) {
+      ios_sdk_path = rebase_path(ios_sdk_path, root_build_dir)
+    }
+    sysroot_flags =
+        "-isysroot $ios_sdk_path -mwatchos-simulator-version-min=$ios_sdk_min"
+  }
+}
+
 mac_toolchain_suite("clang_x64") {
   toolchain_cpu = "x64"
   toolchain_os = "mac"
diff --git a/runtime/BUILD.gn b/runtime/BUILD.gn
index d3d06a78b55..9db127b03c7 100644
--- a/runtime/BUILD.gn
+++ b/runtime/BUILD.gn
@@ -104,6 +104,14 @@ config("dart_os_config") {
   } else if (target_os == "ios") {
     defines += [ "DART_TARGET_OS_MACOS" ]
     defines += [ "DART_TARGET_OS_MACOS_IOS" ]
+  } else if (target_os == "watchos") {
+    defines += [ "DART_TARGET_OS_MACOS" ]
+
+    # This doesn't look entirely correct, but so far it looks
+    # sufficient and allows to add watchOS support with less changes.
+    # If we need to differentiate iOS and watchOS targets later, we'll
+    # change this.
+    defines += [ "DART_TARGET_OS_MACOS_IOS" ]
   } else if (target_os == "linux") {
     defines += [ "DART_TARGET_OS_LINUX" ]
   } else if (target_os == "mac") {
@@ -317,7 +325,10 @@ source_set("dart_api") {
 
 library_for_all_configs("libdart") {
   target_type = dart_component_kind
-  extra_nonproduct_deps = [ "vm:libprotozero" ]
+  extra_nonproduct_deps = []
+  if (dart_support_perfetto) {
+    extra_nonproduct_deps += [ "vm:libprotozero" ]
+  }
   extra_deps = [
     ":generate_version_cc_file",
     "../third_party/double-conversion/src:libdouble_conversion",
diff --git a/runtime/bin/process_macos.cc b/runtime/bin/process_macos.cc
index 5f3c8a5f316..7ebcf63b085 100644
--- a/runtime/bin/process_macos.cc
+++ b/runtime/bin/process_macos.cc
@@ -903,6 +903,11 @@ int Process::Exec(Namespace* namespc,
                   const char* working_directory,
                   char* errmsg,
                   intptr_t errmsg_len) {
+#if defined(DART_HOST_OS_WATCH)
+  // execvp is not available on watchOS.
+  Utils::StrError(ENOSYS, errmsg, errmsg_len);
+  return -1;
+#else
   if (working_directory != nullptr &&
       TEMP_FAILURE_RETRY(chdir(working_directory)) == -1) {
     Utils::StrError(errno, errmsg, errmsg_len);
@@ -912,6 +917,7 @@ int Process::Exec(Namespace* namespc,
   execvp(const_cast<const char*>(path), const_cast<char* const*>(arguments));
   Utils::StrError(errno, errmsg, errmsg_len);
   return -1;
+#endif
 }
 
 static int SignalMap(intptr_t id) {
diff --git a/runtime/platform/globals.h b/runtime/platform/globals.h
index 2996d476b08..00b22c133de 100644
--- a/runtime/platform/globals.h
+++ b/runtime/platform/globals.h
@@ -122,6 +122,9 @@
 #if TARGET_OS_IPHONE
 #define DART_HOST_OS_IOS 1
 #endif
+#if TARGET_OS_WATCH
+#define DART_HOST_OS_WATCH 1
+#endif
 
 #elif defined(_WIN32)
 
diff --git a/runtime/runtime_args.gni b/runtime/runtime_args.gni
index 9ee225d137d..feebf8efc02 100644
--- a/runtime/runtime_args.gni
+++ b/runtime/runtime_args.gni
@@ -72,11 +72,14 @@ declare_args() {
   # Whether the sampling heap profiler should be included in product mode.
   dart_include_sampling_heap_profiler = false
 
-  # Whether features that depend on Perfetto should be built. We temporarily
-  # need to define this to allow excluding code that depends on Perfetto from
-  # being built on platforms which have a problem linking in the Perfetto
-  # library.
-  dart_support_perfetto = true
+  # Whether features that depend on Perfetto should be built. We need
+  # to define this to allow excluding code that depends on Perfetto
+  # from being built on platforms which have a problem linking in the
+  # Perfetto library, e.g. watchOS.
+  #
+  # is_watchos may be undefined when Dart SDK is built from the Flutter
+  # engine tree.
+  dart_support_perfetto = !defined(is_watchos) || !is_watchos
 
   # Whether to support dynamic loading and interpretation of Dart bytecode.
   dart_dynamic_modules = false
diff --git a/runtime/tools/bin_to_assembly.py b/runtime/tools/bin_to_assembly.py
index 6e3b373d823..888d2d7b329 100755
--- a/runtime/tools/bin_to_assembly.py
+++ b/runtime/tools/bin_to_assembly.py
@@ -51,7 +51,7 @@ def Main():
         return -1
 
     with open(options.output, "w") as output_file:
-        if options.target_os in ["mac", "ios"]:
+        if options.target_os in ["mac", "ios", "watchos"]:
             if options.executable:
                 output_file.write(".text\n")
             else:
@@ -106,7 +106,7 @@ def Main():
                 if incbin:
                     output_file.write(".incbin \"%s\"\n" % options.input)
 
-        if options.target_os not in ["mac", "ios", "win", "win_gnu"]:
+        if options.target_os not in ["mac", "ios", "watchos", "win", "win_gnu"]:
             output_file.write(".size {0}, .-{0}\n".format(options.symbol_name))
 
         if options.size_symbol_name:
@@ -128,7 +128,7 @@ def Main():
                 else:
                     output_file.write("dword %d\n" % size)
             else:
-                if options.target_os in ["mac", "ios"]:
+                if options.target_os in ["mac", "ios", "watchos"]:
                     output_file.write(
                         ".global _%s\n" % options.size_symbol_name)
                     output_file.write("_%s:\n" % options.size_symbol_name)
diff --git a/runtime/vm/BUILD.gn b/runtime/vm/BUILD.gn
index f4be2d999f9..19cfec7d866 100644
--- a/runtime/vm/BUILD.gn
+++ b/runtime/vm/BUILD.gn
@@ -172,7 +172,10 @@ source_set("libprotozero") {
 library_for_all_configs("libdart_vm") {
   target_type = "source_set"
   extra_product_deps = []
-  extra_nonproduct_deps = [ ":libprotozero" ]
+  extra_nonproduct_deps = []
+  if (dart_support_perfetto) {
+    extra_nonproduct_deps += [ ":libprotozero" ]
+  }
   extra_deps = [
     "//third_party/icu:icui18n",
     "//third_party/icu:icuuc",
@@ -213,7 +216,11 @@ library_for_all_configs_with_compiler("libdart_compiler") {
   public_configs = [ ":libdart_vm_config" ]
   sources = rebase_path(compiler_sources, ".", "./compiler/")
   include_dirs = [ ".." ]
-  extra_nonproduct_deps = [ ":libprotozero" ]
+
+  extra_nonproduct_deps = []
+  if (dart_support_perfetto) {
+    extra_nonproduct_deps += [ ":libprotozero" ]
+  }
   extra_deps = []
   if (is_fuchsia) {
     extra_deps += [ "$fuchsia_sdk/pkg/trace-engine" ]
@@ -222,7 +229,10 @@ library_for_all_configs_with_compiler("libdart_compiler") {
 
 library_for_all_configs("libdart_lib") {
   target_type = "source_set"
-  extra_nonproduct_deps = [ ":libprotozero" ]
+  extra_nonproduct_deps = []
+  if (dart_support_perfetto) {
+    extra_nonproduct_deps += [ ":libprotozero" ]
+  }
   extra_deps = []
   if (is_fuchsia) {
     extra_deps += [ "$fuchsia_sdk/pkg/trace-engine" ]
diff --git a/runtime/vm/thread_interrupter_macos.cc b/runtime/vm/thread_interrupter_macos.cc
index e9243a24973..0d07da01a09 100644
--- a/runtime/vm/thread_interrupter_macos.cc
+++ b/runtime/vm/thread_interrupter_macos.cc
@@ -49,7 +49,11 @@ class ThreadInterrupterMacOS {
     ASSERT(os_thread != nullptr);
     mach_thread_ = pthread_mach_thread_np(os_thread->id());
     ASSERT(reinterpret_cast<void*>(mach_thread_) != nullptr);
+#if !defined(DART_HOST_OS_WATCH)
     res = thread_suspend(mach_thread_);
+#else
+    res = KERN_FAILURE;
+#endif
   }
 
   void CollectSample() {
@@ -58,9 +62,14 @@ class ThreadInterrupterMacOS {
     }
     auto count = static_cast<mach_msg_type_number_t>(THREAD_STATE_FLAVOR_SIZE);
     thread_state_flavor_t state;
+#if !defined(DART_HOST_OS_WATCH)
     kern_return_t res =
         thread_get_state(mach_thread_, THREAD_STATE_FLAVOR,
                          reinterpret_cast<thread_state_t>(&state), &count);
+#else
+    USE(count);
+    kern_return_t res = KERN_FAILURE;
+#endif
     ASSERT(res == KERN_SUCCESS);
     Thread* thread = static_cast<Thread*>(os_thread_->thread());
     if (thread == nullptr) {
@@ -74,7 +83,11 @@ class ThreadInterrupterMacOS {
     if (res != KERN_SUCCESS) {
       return;
     }
+#if !defined(DART_HOST_OS_WATCH)
     res = thread_resume(mach_thread_);
+#else
+    res = KERN_FAILURE;
+#endif
     ASSERT(res == KERN_SUCCESS);
   }
 
diff --git a/tools/gn.py b/tools/gn.py
index dcb48883b2e..752c6aa59d2 100755
--- a/tools/gn.py
+++ b/tools/gn.py
@@ -198,7 +198,12 @@ def ToGnArgs(args, mode, arch, target_os, sanitizer, verify_sdk_hash,
         gn_args['target_os'] = host_os
     elif target_os == 'ios_simulator':
         gn_args['target_os'] = 'ios'
-        gn_args['use_ios_simulator'] = True
+        gn_args['use_simulator'] = True
+    elif target_os == 'watchos_simulator':
+        gn_args['target_os'] = 'watchos'
+        gn_args['use_simulator'] = True
+    elif target_os == 'watchos':
+        gn_args['target_os'] = 'watchos'
     else:
         gn_args['target_os'] = target_os
 
@@ -358,7 +363,7 @@ def ProcessOptions(args):
     for os_name in oses:
         if not os_name in [
                 'android', 'freebsd', 'linux', 'macos', 'win32', 'fuchsia',
-                'ios', 'ios_simulator'
+                'ios', 'ios_simulator', 'watchos', 'watchos_simulator'
         ]:
             print("Unknown os %s" % os_name)
             return False
@@ -393,7 +398,7 @@ def ProcessOptions(args):
                     "Cross-compilation to %s is not supported for architecture %s."
                     % (os_name, arch))
                 return False
-        elif os_name == 'ios' or os_name == 'ios_simulator':
+        elif os_name == 'ios' or os_name == 'ios_simulator' or os_name == 'watchos' or os_name == 'watchos_simulator':
             if not HOST_OS in ['macos']:
                 print(f'Target os {os_name} is only supported on macOS')
                 return False
diff --git a/tools/utils.py b/tools/utils.py
index d8d5200369e..b7686afdd81 100644
--- a/tools/utils.py
+++ b/tools/utils.py
@@ -339,6 +339,8 @@ def GetBuildConf(mode, arch, conf_os=None, sanitizer=None):
         os_fragment = conf_os.title()
         if (conf_os == 'ios_simulator'):
             os_fragment = 'IosSim'
+        if (conf_os == 'watchos_simulator'):
+            os_fragment = 'WatchosSim'
         return '{}{}{}'.format(GetBuildMode(mode), os_fragment, arch.upper())
 
     # Ask for a cross build if the host and target architectures don't match.
diff --git a/utils/aot_snapshot.gni b/utils/aot_snapshot.gni
index 138e6baf011..032adeb3dbf 100644
--- a/utils/aot_snapshot.gni
+++ b/utils/aot_snapshot.gni
@@ -177,7 +177,7 @@ template("aot_snapshot") {
     output_prefix = "lib"
     output_extension = ""
 
-    if (current_os == "mac" || current_os == "ios") {
+    if (current_os == "mac" || current_os == "ios" || current_os == "watchos") {
       output_extension = "dylib"
     } else if (current_os == "win") {
       output_extension = "dll"