diff --git a/proposals/template.md b/proposals/template.md
index 0de0e64a2522..edc51d50b99b 100644
--- a/proposals/template.md
+++ b/proposals/template.md
@@ -23,6 +23,8 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 ## TODO: Initial proposal setup
 
+> TIP: Run `../src/scripts/new-proposal.py "TITLE"` to do new proposal setup.
+
 1. Copy this template to `new.md`, and create a commit.
 2. Create a GitHub pull request, to get a pull request number.
    - Add the `proposal` and `WIP` labels to the pull request.
diff --git a/src/scripts/new-proposal.py b/src/scripts/new-proposal.py
new file mode 100755
index 000000000000..d0ef228dde51
--- /dev/null
+++ b/src/scripts/new-proposal.py
@@ -0,0 +1,159 @@
+#!/usr/bin/env python3
+
+"""Prepares a new proposal file and PR."""
+
+__copyright__ = """
+Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+Exceptions. See /LICENSE for license information.
+SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+"""
+
+import os
+import re
+import shlex
+import shutil
+import subprocess
+import sys
+
+_USAGE = """Usage:
+  ./new-proposal.py <title> [<branch>]
+
+Generates a branch and PR for a new proposal with the specified title.
+"""
+
+_PROMPT = """This will:
+  - Create and switch to a new branch named '%s'.
+  - Create a new proposal titled '%s'.
+  - Create a PR for the proposal.
+
+Continue? (Y/n) """
+
+
+def _FillTemplate(template_path, title, pr_num):
+    """Fills out template TODO fields."""
+    with open(template_path) as template_file:
+        content = template_file.read()
+    content = re.sub(r"^# TODO\n", "# %s\n" % title, content)
+    content = re.sub(
+        r"(https://github.com/[^/]+/[^/]+/pull/)####",
+        r"\g<1>%d" % pr_num,
+        content,
+    )
+    content = re.sub(r"## TODO(?:.|\n)*(## Problem)", r"\1", content)
+    return content
+
+
+def _Run(argv, check=True):
+    """Runs a command."""
+    cmd = " ".join([shlex.quote(x) for x in argv])
+    print("\n+ RUNNING: %s" % cmd, file=sys.stderr)
+    p = subprocess.run(argv)
+    if check and p.returncode != 0:
+        sys.exit("ERROR: Command failed: %s" % cmd)
+
+
+def _RunPRCreate(argv):
+    """Runs a command and returns the PR#."""
+    cmd = " ".join([shlex.quote(x) for x in argv])
+    print("\n+ RUNNING: %s" % cmd, file=sys.stderr)
+    p = subprocess.Popen(argv, stdout=subprocess.PIPE)
+    out, _ = p.communicate()
+    out = out.decode("utf-8")
+    print(out, end="")
+    if p.returncode != 0:
+        sys.exit("ERROR: Command failed: %s" % cmd)
+    match = re.search(
+        r"^https://github.com/[^/]+/[^/]+/pull/(\d+)$", out, re.MULTILINE
+    )
+    if not match:
+        sys.exit("ERROR: Failed to find PR# in output.")
+    return int(match[1])
+
+
+if __name__ == "__main__":
+    # Require an argument.
+    if len(sys.argv) not in (2, 3):
+        sys.exit(_USAGE)
+    title = sys.argv[1]
+    branch = None
+    if len(sys.argv) == 3:
+        branch = sys.argv[2]
+
+    # Verify git and gh are available.
+    git_bin = shutil.which("git")
+    if not git_bin:
+        sys.exit("ERROR: Missing `git` CLI.")
+    gh_bin = shutil.which("gh")
+    if not gh_bin:
+        sys.exit("ERROR: Missing `gh` CLI.")
+    precommit_bin = shutil.which("pre-commit")
+    if not precommit_bin:
+        sys.exit("ERROR: Missing `pre-commit` CLI.")
+
+    # Ensure a good working directory.
+    proposals_dir = os.path.realpath(
+        os.path.join(os.path.dirname(__file__), "../../proposals")
+    )
+    os.chdir(proposals_dir)
+
+    # Verify there are no uncommitted changes.
+    p = subprocess.run([git_bin, "diff-index", "--quiet", "HEAD", "--"])
+    if p.returncode != 0:
+        sys.exit("ERROR: There are uncommitted changes in your git repo.")
+
+    # Only use the first 20 chars of the title for branch names.
+    if not branch:
+        branch = "proposal-%s" % (title.lower().replace(" ", "-")[0:20])
+
+    # Prompt before proceeding.
+    response = "?"
+    while response not in ("y", "n", ""):
+        response = input(_PROMPT % (branch, title)).lower()
+    if response == "n":
+        sys.exit("ERROR: Cancelled")
+
+    # Create a proposal branch.
+    _Run([git_bin, "checkout", "-b", branch, "trunk"])
+    _Run([git_bin, "push", "-u", "origin", branch])
+
+    # Copy template.md to a temp file.
+    template_path = os.path.join(proposals_dir, "template.md")
+    temp_path = os.path.join(proposals_dir, "new-proposal.tmp")
+    shutil.copyfile(template_path, temp_path)
+    _Run([git_bin, "add", temp_path])
+    _Run([git_bin, "commit", "-m", "Creating new proposal: %s" % title])
+
+    # Create a PR with WIP+proposal labels.
+    _Run([git_bin, "push"])
+    pr_num = _RunPRCreate(
+        [
+            gh_bin,
+            "pr",
+            "create",
+            "--label",
+            "WIP,proposal",
+            "--title",
+            title,
+            "--body",
+            "",
+        ]
+    )
+
+    # Remove the temp file, create p####.md, and fill in PR information.
+    os.remove(temp_path)
+    final_path = os.path.join(proposals_dir, "p%04d.md" % pr_num)
+    content = _FillTemplate(template_path, title, pr_num)
+    with open(final_path, "w") as final_file:
+        final_file.write(content)
+    _Run([git_bin, "add", temp_path, final_path])
+    _Run([precommit_bin, "run"], check=False)  # Needs a ToC update.
+    _Run([git_bin, "add", final_path, os.path.join(proposals_dir, "README.md")])
+    _Run([git_bin, "commit", "-m", "Filling out template with PR %d" % pr_num])
+
+    # Push the PR update.
+    _Run([git_bin, "push"])
+
+    print(
+        "\nCreated PR %d for %s. Make changes to:\n  %s"
+        % (pr_num, title, final_path)
+    )