From 1974 to 1976, Keenan was an assistant commonwealth's attorney for Fairfax County, Virginia, before entering private practice, first as a solo practitioner and then as partner in the firm Keenan, Ardis and Roehrenbeck. In 1980, she was made a judge of the General District Court of Fairfax County, and two years later became the first woman to be elected to a Circuit Court judgeship by the Virginia General Assembly. In 1985, she was elected as one of the first ten judges of the newly created Court of Appeals of Virginia, making her the first woman to serve as a state appellate court judge in Virginia. She is the first woman to serve on all levels of the Virginia court system. In 2011, she wrote the foreword to the first volume of Jurist Prudent, the collected opinions of her former Supreme Court of Virginia colleague Sr. Justice Lawrence L. Koontz, Jr.
Service on the Supreme Court of Virginia
In 1991 Keenan was elected to be a Justice of the Supreme Court of Virginia, succeeding Justice Charles S. Russell. She was reelected in 2003 to a second 12-year term on the Court. She is the only Virginia jurist to serve at every level of Virginia's judicial system. Sr. Justices Lawrence L. Koontz, Jr. and Leroy F. Millette, Jr. and Justice Cleo Powell have also served at every level of the state's court system. She joins Judge G. Steven Agee of that court as the second Virginia Supreme Court Justice to advance to the federal appellate bench in recent times.
Federal judicial service
In 2009, Keenan asked to be considered for a seat on the United States Court of Appeals for the Fourth Circuit. The Virginia Bar Association included her name on the list of candidates it submitted to Virginia's two senators on February 24, 2009. On June 2, 2009, Virginia's senators recommended that President Barack Obama nominate her to the Fourth Circuit. On September 14, 2009, Obama formally nominated Keenan to the Fourth Circuit, and the Senate Judiciary Committee backed her nomination. On February 26, 2010, Senate Majority LeaderHarry Reid filed for cloture on Keenan's nomination. The Senate voted 99–0 for cloture on the nomination on March 2, 2010. She was confirmed in a 99–0 vote later that day. She received her commission on March 9, 2010.
Notable case(s)
In Seay v. Cannon, on June 21, 2019, Keenan, who was joined by A. Marvin Quattlebaum Jr., ruled that double jeopardy bars retrial after a mistrial is granted over a defendant's objection. Paul V. Niemeyer dissented. On March 30, 2020, the Supreme Court denied certiorari, although Justices Thomas, Alito, and Kavanaugh would have granted cert to the case.