Mary Margaret McKeown (born May 11, 1951) is a Senior United States circuit judge of the United States Court of Appeals for the Ninth Circuit based in San Diego. McKeown has served on the Ninth Circuit since her confirmation in 1998.
 McKeown, a native of Casper, Wyoming, graduated from Kelly Walsh High School in Casper in 1969. She attended the University of Madrid and graduated Phi Beta Kappa from the University of Wyoming with a Bachelor of Arts in 1972.
 She worked for Senator Clifford P. Hansen, whom she credits with inspiring her interest in the legal profession. McKeown  received her Juris Doctor in 1975 from Georgetown University Law Center. She also received an honorary Doctor of Laws from Georgetown.
 McKeown was the first female partner with the law firm of Perkins Coie in Seattle and Washington, D.C. McKeown specialized in intellectual property, antitrust, trade regulation, and complex litigation, representing clients like Boeing, Nintendo, Amazon, and Citicorp. McKeown was co-founder of the firm’s Washington, D.C. office and founded the firm’s intellectual property practice. She spent over two decades at the firm.
 From 1980 until 1981, McKeown served as a White House Fellow. She worked as a Special Assistant to Secretary of the Interior Cecil D. Andrus and as Special Assistant for domestic policy at the White House.
 McKeown was the president of the Federal Bar Association of the Western District of Washington and a founder and first co-president of the statewide Washington Women Lawyers.
 McKeown is the jurist-in-residence at the University of San Diego (USD) School of Law.
 She taught at Georgetown University Law Center, Northwestern University Law School, and the University of Washington School of Law. McKeown is an affiliated scholar at the Center for the American West at Stanford University.
 Selected publications include: "The Lost Sanctuary: Examining Sex Trafficking Through the Lens of Ah Sou" (Cornell Journal of International Law, 2008); "Happy Birthday Statute of Anne: The Dance Between the Courts and Congress" (Berkeley Technology Law Journal, 2010); "To Judge or Not to Judge: Transparency and Recusal in the Federal System" (The Review of Litigation, 2011); "The Internet and the Constitution: A Selective Retrospective" (Washington Journal of Law, Technology & Arts, 2014); "Culinary Ambiguity: A Canonical Approach to Deciphering Menus" (Harvard Journal on Legislation, 2014); "Beginning with Brown: Springboard for Gender Equality and Social Change" (San Diego Law Review, Fall 2015); "The ABA Rule of Law Initiative: Celebrating 25 Years of Global Initiatives" (Michigan Journal of International Law, 2018); "The Nineteenth Amendment Centennial Cookbook: 100 Recipes for 100 Years" (ABA 2019); "My Mother Made Me Do It: A Short History of the Nineteenth Amendment" (Litigation, 2020); "The Judiciary Steps Up to the Workplace Challenge" (Northwestern University Law Review, 2021); and "Politics and Judicial Ethics: A Historical Perspective" (Yale Law Journal Forum, 2021).
 She is the author of Citizen Justice: The Environmental Legacy of Justice William O. Douglas—Public Advocate and Conservation Champion (Potomac Press 2022).
 On March 29, 1996, President Bill Clinton nominated McKeown for a seat on the United States Court of Appeals for the Ninth Circuit, and then renominated her on January 7, 1997. McKeown was confirmed by the United States Senate on March 27, 1998, by a 80–11 vote. She received her commission on April 8, 1998. 
On January 12, 2022, McKeown announced that she would assume senior status upon the confirmation of her successor.
On September 15, 2022, she assumed senior status.
 She has served on multiple committees for the court. For the Ninth Circuit, she currently[when?] serves as chair of the Workplace Environment Committee and chair of the Pacific Islands Committee. She has also served on the Executive Committee of the Ninth Circuit, chair of the Ninth Circuit Judicial Conference, the Ad Hoc Death Penalty Rules Committee, and chair of the Ninth Circuit Education Commission.
 She served as chair of the Judicial Conference of the United States Codes of Conduct Committee, the national ethics committee for federal judges, and is currently[when?] a member of the Judicial Conference of the United States Committee on Judicial Conduct and Disability. McKeown served as a member of the ABA Commission to redraft the Model Code of Judicial Ethics.
 McKeown has worked on promoting a respectful work environment within the judiciary through her position as Chair of the Workplace Environment Committee for the Ninth Circuit and her appointment by Chief Justice Roberts to the Federal Judiciary Workplace Conduct Working Group.
 She is former president of the Federal Judges Association and the San Diego Association of Business Trial Lawyers. She served as chair of the ABA Commission on the Nineteenth Amendment and the ABA Standing Committee on Federal Judicial Improvements. She has also served on the Managerial Board of the International Association of Women Judges.
 Between December 2014 and August 2020, McKeown sat on an en banc panel 29 times. McKeown was in the majority in all 29 of the en banc cases she heard during that period. She has also authored more than 600 opinions.
 McKeown is the recipient of the: American Inns of Court Professionalism Award for the Ninth Circuit; ABA John Marshall Award; ABA Margaret Brent Women of Achievement Award; Big Sisters Outstanding Mentor Award; California Bar Association Intellectual Property Vanguard Award; Federal Bar Association Public Service Award; Georgetown University Law Center Robert F. Drinan Public Service Award; Georgetown University Law Center Outstanding Alumnae; Georgetown University John Carroll Award (highest honor); Girl Scouts Cool Women Award; University of Wyoming Distinguished Alumni Award; Washington Women Lawyers’ President’s Award; White House Fellows Legacy of Leadership Award; and Federal Bar Association Public Service Award.
 In 2020, McKeown was elected to the American Academy of Arts & Sciences. She served as past chair of the White House Fellows Foundation and the Georgetown Law School Board of Visitors. Additionally, she was on the national boards of Volunteers of America and Girl Scouts U.S.A.
 McKeown serves on the board of the Teton Science School in Jackson, Wyoming.
 She participated in the first American mountain climbing expedition to Mount Shishapangma in Tibet.
 McKeown was elected to the American Law Institute in 1993 and was elected to the ALI Council in 2009. She has served as an Adviser on several projects, including: Intellectual Property: Principles Governing Jurisdiction, Choice of Law, and Judgments in Transnational Disputes; Restatement of the U.S. Law of International Commercial Arbitration and Investor-State Arbitration; and Restatement of U.S. Foreign Relations Law. She is also a current Advisor on the Restatement of the Law for Copyright.
 McKeown has lectured and taught throughout the world on intellectual property, international law, human rights law, litigation, ethics, judicial administration, and constitutional law and has participated in numerous rule of law initiatives with judges and lawyers. In 2016, McKeown took part in the 10th annual International Humanitarian Law Dialogs in Nuremberg, Germany, where she presented the Nuremberg Declaration—a joint statement by international prosecutors. McKeown has chaired the American Bar Association’s Rule of Law Initiative and is a senior advisor. She previously chaired ABA ROLI Latin America and the Caribbean Council. She serves on the board of the World Justice Project and on the Judicial Advisory Board of the American Society of International Law.
 In 2022, McKeown published a nonfiction book, Citizen Justice: The Environmental Legacy of William O. Douglas.