Donald Francis McGahn II, commonly known as Don McGahn, is an American lawyer born on June 16, 1968, in Atlantic City, New Jersey, U.S. He grew up in Atlantic City as the son of Noreen (née Rogan) and Donald F. McGahn, and is the nephew of former Democratic New Jersey State Senator Joseph McGahn, who served as medical director at Donald Trump's Resorts International, and Atlantic City attorney Patrick McGahn, who represented Trump's casino interests from 1982 until Trump sued him in 1995 for alleged overbilling. McGahn attended the United States Naval Academy, the University of Notre Dame, Widener University School of Law, and Georgetown University Law Center. Early in his career, he clerked for Judge Charles R. Alexander of the Court of Common Pleas in Pennsylvania, practiced at Patton Boggs LLP, served as general counsel to the National Republican Congressional Committee from 1999 to 2008 and counsel to the Illinois Republican Party, and headed McGahn & Associates PLLC specializing in election law.

McGahn was nominated by President George W. Bush and confirmed unanimously by the Senate to serve as a Commissioner of the Federal Election Commission (FEC) from July 9, 2008, to September 12, 2013, acting as Chairman from July 10 to December 31, 2008. He later became a partner at Patton Boggs (2013) and Jones Day (2013-2017 and 2019-present), where he advises on government regulation, enforcement, and political issues. From January 20, 2017, to October 17, 2018, he served as White House Counsel to President Donald Trump, advising on legal matters including judicial nominations—overseeing the appointment of a record number of federal judges including two Supreme Court justices—deregulation efforts, executive orders, national security, and trade. He was a key architect of the administration's judicial nomination strategy as a prominent conservative lawyer and key Federalist Society member. Post-tenure, he was appointed to the Council of the Administrative Conference of the United States.

McGahn has been involved in notable controversies, including a 2019 court order and 2020 D.C. Circuit ruling (7-2) allowing the House to subpoena his testimony on Trump administration matters despite absolute immunity claims. He was campaign counsel for Trump's 2016 presidential run.