--- a/build/full_test.py
+++ b/build/full_test.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2018 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
--- a/build/gen.py
+++ b/build/gen.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
--- a/infra/recipes.py
+++ b/infra/recipes.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Copyright 2017 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
--- a/src/gn/exec_process_unittest.cc
+++ b/src/gn/exec_process_unittest.cc
@@ -33,7 +33,7 @@
   args.push_back(L"-c");
   args.push_back(base::UTF8ToUTF16(command));
 #else
-  args.push_back("python");
+  args.push_back("python3");
   args.push_back("-c");
   args.push_back(command);
 #endif
--- a/src/gn/setup.cc
+++ b/src/gn/setup.cc
@@ -717,7 +717,7 @@
     }
     build_settings_.set_python_path(python_path.NormalizePathSeparatorsTo('/'));
 #else
-    build_settings_.set_python_path(base::FilePath("python"));
+    build_settings_.set_python_path(base::FilePath("python3"));
 #endif
   }
   return true;
--- a/src/gn/json_project_writer_unittest.cc
+++ b/src/gn/json_project_writer_unittest.cc
@@ -37,7 +37,7 @@
       SubstitutionList::MakeForTest("//out/Debug/output1.out");
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
   std::vector<const Target*> targets;
   targets.push_back(&target);
 #if defined(OS_WIN)
@@ -172,7 +172,7 @@
       SubstitutionList::MakeForTest("//out/Debug/{{source_name_part}}.out");
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
   std::vector<const Target*> targets;
   targets.push_back(&target);
 #if defined(OS_WIN)
--- a/src/gn/ninja_action_target_writer_unittest.cc
+++ b/src/gn/ninja_action_target_writer_unittest.cc
@@ -54,14 +54,14 @@
   ASSERT_TRUE(target.OnResolved(&err));
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
 
   std::ostringstream out;
   NinjaActionTargetWriter writer(&target, out);
   writer.Run();
 
   const char* expected = R"(rule __foo_bar___rule
-  command = /usr/bin/python ../../foo/script.py
+  command = /usr/bin/python3 ../../foo/script.py
   description = ACTION //foo:bar()
   restat = 1
 
@@ -96,7 +96,7 @@
   ASSERT_TRUE(target.OnResolved(&err));
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
 
   std::ostringstream out;
   NinjaActionTargetWriter writer(&target, out);
@@ -105,7 +105,7 @@
   // The console pool's name must be mapped exactly to the string "console"
   // which is a special pre-defined pool name in ninja.
   const char* expected = R"(rule __foo_bar___rule
-  command = /usr/bin/python ../../foo/script.py
+  command = /usr/bin/python3 ../../foo/script.py
   description = ACTION //foo:bar()
   restat = 1
 
@@ -138,7 +138,7 @@
   ASSERT_TRUE(target.OnResolved(&err));
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
 
   std::ostringstream out;
   NinjaActionTargetWriter writer(&target, out);
@@ -146,7 +146,7 @@
 
   const char expected_linux[] =
       "rule __foo_bar___rule\n"
-      "  command = /usr/bin/python ../../foo/script.py\n"
+      "  command = /usr/bin/python3 ../../foo/script.py\n"
       "  description = ACTION //foo:bar()\n"
       "  restat = 1\n"
       "\n"
@@ -198,7 +198,7 @@
   ASSERT_TRUE(target.OnResolved(&err));
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
 
   std::ostringstream out;
   NinjaActionTargetWriter writer(&target, out);
@@ -206,7 +206,7 @@
 
   const char expected_linux[] =
       "rule __foo_bar___rule\n"
-      "  command = /usr/bin/python ../../foo/script.py -i ${in} "
+      "  command = /usr/bin/python3 ../../foo/script.py -i ${in} "
 // Escaping is different between Windows and Posix.
 #if defined(OS_WIN)
       "\"--out=foo$ bar${source_name_part}.o\"\n"
@@ -263,7 +263,7 @@
   target.config_values().inputs().push_back(SourceFile("//foo/included.txt"));
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
 
   std::ostringstream out;
   NinjaActionTargetWriter writer(&target, out);
@@ -271,7 +271,7 @@
 
   const char expected_linux[] =
       "rule __foo_bar___rule\n"
-      "  command = /usr/bin/python ../../foo/script.py -i ${in} "
+      "  command = /usr/bin/python3 ../../foo/script.py -i ${in} "
 #if defined(OS_WIN)
       "\"--out=foo$ bar${source_name_part}.o\"\n"
 #else
@@ -318,7 +318,7 @@
       SubstitutionList::MakeForTest("//out/Debug/{{source_name_part}}.out");
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
 
   std::ostringstream out;
   NinjaActionTargetWriter writer(&target, out);
@@ -331,7 +331,7 @@
       // These come from rsp_file_contents above.
       "  rspfile_content = -j ${source_name_part}\n"
       // These come from the args.
-      "  command = /usr/bin/python ../../foo/script.py ${in} "
+      "  command = /usr/bin/python3 ../../foo/script.py ${in} "
       "${source_file_part} ${rspfile}\n"
       "  description = ACTION //foo:bar()\n"
       "  restat = 1\n"
@@ -376,7 +376,7 @@
       SubstitutionList::MakeForTest("//out/Debug/{{source_name_part}}.out");
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
 
   std::ostringstream out;
   NinjaActionTargetWriter writer(&target, out);
@@ -385,7 +385,7 @@
   const char expected_linux[] =
       "rule __foo_bar___rule\n"
       // These come from the args.
-      "  command = /usr/bin/python ../../foo/script.py ${in} "
+      "  command = /usr/bin/python3 ../../foo/script.py ${in} "
       "${source_file_part}\n"
       "  description = ACTION //foo:bar()\n"
       "  restat = 1\n"
@@ -405,7 +405,7 @@
   TestWithScope setup;
 
   setup.build_settings()->set_python_path(
-      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python")));
+      base::FilePath(FILE_PATH_LITERAL("/usr/bin/python3")));
 
   Target dep(setup.settings(), Label(SourceDir("//foo/"), "dep"));
   dep.set_output_type(Target::ACTION);
@@ -432,7 +432,7 @@
     const char expected_linux[] =
         "rule __foo_foo___rule\n"
         // These come from the args.
-        "  command = /usr/bin/python ../../foo/script.py\n"
+        "  command = /usr/bin/python3 ../../foo/script.py\n"
         "  description = ACTION //foo:foo()\n"
         "  restat = 1\n"
         "\n"
@@ -461,7 +461,7 @@
     const char expected_linux[] =
         "rule __bar_bar___rule\n"
         // These come from the args.
-        "  command = /usr/bin/python ../../bar/script.py\n"
+        "  command = /usr/bin/python3 ../../bar/script.py\n"
         "  description = ACTION //bar:bar()\n"
         "  restat = 1\n"
         "\n"