diff --git a/clang-tools-extra/clang-tidy/tool/run-clang-tidy.py b/clang-tools-extra/clang-tidy/tool/run-clang-tidy.py
--- a/clang-tools-extra/clang-tidy/tool/run-clang-tidy.py
+++ b/clang-tools-extra/clang-tidy/tool/run-clang-tidy.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 #===- run-clang-tidy.py - Parallel clang-tidy runner --------*- python -*--===#
 #
@@ -41,6 +41,7 @@
 import json
 import multiprocessing
 import os
+import queue
 import re
 import shutil
 import subprocess
@@ -54,13 +55,6 @@
 except ImportError:
   yaml = None
 
-is_py2 = sys.version[0] == '2'
-
-if is_py2:
-    import Queue as queue
-else:
-    import queue as queue
-
 
 def strtobool(val):
   """Convert a string representation of truth to a bool following LLVM's CLI argument parsing."""
@@ -158,20 +152,29 @@
     open(mergefile, 'w').close()
 
 
-def check_clang_apply_replacements_binary(args):
-  """Checks if invoking supplied clang-apply-replacements binary works."""
-  try:
-    subprocess.check_call([args.clang_apply_replacements_binary, '--version'])
-  except:
-    print('Unable to run clang-apply-replacements. Is clang-apply-replacements '
-          'binary correctly specified?', file=sys.stderr)
-    traceback.print_exc()
-    sys.exit(1)
+def find_binary(arg, name, build_path):
+  """Get the path for a binary or exit"""
+  if arg:
+    if shutil.which(arg):
+      return arg
+    else:
+      raise SystemExit(
+        "error: passed binary '{}' was not found or is not executable"
+        .format(arg))
 
+  built_path = os.path.join(build_path, "bin", name)
+  binary = shutil.which(name) or shutil.which(built_path)
+  if binary:
+    return binary
+  else:
+    raise SystemExit(
+      "error: failed to find {} in $PATH or at {}"
+      .format(name, built_path))
 
-def apply_fixes(args, tmpdir):
+
+def apply_fixes(args, clang_apply_replacements_binary, tmpdir):
   """Calls clang-apply-fixes on a given directory."""
-  invocation = [args.clang_apply_replacements_binary]
+  invocation = [clang_apply_replacements_binary]
   if args.format:
     invocation.append('-format')
   if args.style:
@@ -180,11 +183,12 @@
   subprocess.call(invocation)
 
 
-def run_tidy(args, tmpdir, build_path, queue, lock, failed_files):
+def run_tidy(args, clang_tidy_binary, tmpdir, build_path, queue, lock,
+             failed_files):
   """Takes filenames out of queue and runs clang-tidy on them."""
   while True:
     name = queue.get()
-    invocation = get_tidy_invocation(name, args.clang_tidy_binary, args.checks,
+    invocation = get_tidy_invocation(name, clang_tidy_binary, args.checks,
                                      tmpdir, build_path, args.header_filter,
                                      args.allow_enabling_alpha_checkers,
                                      args.extra_arg, args.extra_arg_before,
@@ -210,15 +214,13 @@
   parser = argparse.ArgumentParser(description='Runs clang-tidy over all files '
                                    'in a compilation database. Requires '
                                    'clang-tidy and clang-apply-replacements in '
-                                   '$PATH.')
+                                   '$PATH or in your build directory.')
   parser.add_argument('-allow-enabling-alpha-checkers',
                       action='store_true', help='allow alpha checkers from '
                                                 'clang-analyzer.')
   parser.add_argument('-clang-tidy-binary', metavar='PATH',
-                      default='clang-tidy',
                       help='path to clang-tidy binary')
   parser.add_argument('-clang-apply-replacements-binary', metavar='PATH',
-                      default='clang-apply-replacements',
                       help='path to clang-apply-replacements binary')
   parser.add_argument('-checks', default=None,
                       help='checks filter, when not specified, use clang-tidy '
@@ -278,8 +280,18 @@
     # Find our database
     build_path = find_compilation_database(db_path)
 
+  clang_tidy_binary = find_binary(args.clang_tidy_binary, "clang-tidy",
+                                  build_path)
+
+  tmpdir = None
+  if args.fix or (yaml and args.export_fixes):
+    clang_apply_replacements_binary = find_binary(
+      args.clang_apply_replacements_binary, "clang-apply-replacements",
+      build_path)
+    tmpdir = tempfile.mkdtemp()
+
   try:
-    invocation = get_tidy_invocation("", args.clang_tidy_binary, args.checks,
+    invocation = get_tidy_invocation("", clang_tidy_binary, args.checks,
                                      None, build_path, args.header_filter,
                                      args.allow_enabling_alpha_checkers,
                                      args.extra_arg, args.extra_arg_before,
@@ -306,11 +318,6 @@
   if max_task == 0:
     max_task = multiprocessing.cpu_count()
 
-  tmpdir = None
-  if args.fix or (yaml and args.export_fixes):
-    check_clang_apply_replacements_binary(args)
-    tmpdir = tempfile.mkdtemp()
-
   # Build up a big regexy filter from all command line arguments.
   file_name_re = re.compile('|'.join(args.files))
 
@@ -323,7 +330,8 @@
     lock = threading.Lock()
     for _ in range(max_task):
       t = threading.Thread(target=run_tidy,
-                           args=(args, tmpdir, build_path, task_queue, lock, failed_files))
+                           args=(args, clang_tidy_binary, tmpdir, build_path,
+                                 task_queue, lock, failed_files))
       t.daemon = True
       t.start()
 
@@ -357,7 +365,7 @@
   if args.fix:
     print('Applying fixes ...')
     try:
-      apply_fixes(args, tmpdir)
+      apply_fixes(args, clang_apply_replacements_binary, tmpdir)
     except:
       print('Error applying fixes.\n', file=sys.stderr)
       traceback.print_exc()