Mark Robert Warner (born December 15, 1954) is an American businessman and politician serving as the senior United States senator from Virginia, a seat he has held since 2009. A member of the Democratic Party, Warner served as the 69th governor of Virginia from 2002 to 2006. He is vice chair of the Senate Democratic Caucus and vice chair of the Senate Intelligence Committee.

In 2006, Warner was widely expected to pursue the Democratic nomination in the 2008 U.S. presidential election, but he announced in October 2006 that he would not run, citing a desire not to disrupt his family life. Warner delivered the keynote address at the 2008 Democratic National Convention, and was considered to be a potential vice presidential candidate until he took himself out of consideration after winning the Democratic nomination for the U.S. Senate.

Warner was elected to the Senate in 2008 and reelected in 2014 and 2020. He became Virginia's senior senator in 2013, when Senator Jim Webb retired. He is the honorary chairman of Forward Together PAC.

Before entering politics, Warner became involved in telecommunications-related venture capital during the 1980s. He founded and led the Columbia Capital firm. He also co-founded Capital Cellular Corporation. With a net worth of $214.1 million, Warner is the third-wealthiest member of Congress and its wealthiest Democrat.