Mark Robert Warner (born December 15, 1954) is an American politician and businessman, currently serving in the United States Senate as the junior senator from the Commonwealth of Virginia. He is a member of the Democratic Party. Warner was the 69th governor of Virginia from 2002 to 2006 and is the honorary chairman of the Forward Together PAC. Warner delivered the keynote address before the nation at the 2008 Democratic National Convention. Mark Warner's experience as a congressional staffer and Democratic Party fundraiser in the 1980s prompted his involvement in telecommunications venture capital; he founded the firm Columbia Capital.

In 2006 he was widely expected to pursue the Democratic nomination in the 2008 U.S. presidential elections; however, he announced in October 2006 that he would not run, citing a desire not to disrupt his family life. Warner was considered to be a potential vice presidential pick, but upon receiving the Democratic nomination for the U.S. Senate he announced that he "will not accept any other opportunity." He is expected to become the state's senior senator when Jim Webb retires from the Senate in January 2013. He currently serves on the board of National Democratic Institute for International Affairs.

Warner was born in Indianapolis, Indiana; he is the son of Robert and Marge Warner, and is the older brother of Lisa Warner. He grew up in Illinois, and later in Vernon, Connecticut, where he graduated from Rockville High School. He attributes his interest in politics to his eighth grade social studies teacher, Jim Tyler, who "inspired him to work for social and political change during the tumultuous year of 1968." Warner was class president for three years at Rockville High School and hosted a weekly pick-up basketball game at his house, "a tradition that continues today."