Maria Ellen Cantwell (born October 13, 1958) is an American politician and former businesswoman serving as the junior United States senator from Washington since 2001. A member of the Democratic Party, she served in the Washington House of Representatives from 1987 to 1993, and in the United States House of Representatives from Washington's 1st congressional district from 1993 to 1995.

Born and raised in Indianapolis, Indiana, Cantwell graduated from Miami University before moving to Seattle to work on Alan Cranston's 1984 presidential campaign. In 1986, she was elected to the state House of Representatives, where she served until her election to Congress in 1992. Cantwell served one term in Congress before losing her seat to Republican Rick White in the 1994 election. She then briefly worked in the private sector as vice president of marketing for RealNetworks.

Despite having vowed to remain out of politics, Cantwell ran for the United States Senate in 2000. She defeated Republican incumbent Slade Gorton in one of the closest elections in the state's history. Cantwell was reelected in 2006, 2012, and 2018. Upon the February 2017 resignation of Jeff Sessions to become United States Attorney General, she became the most senior junior senator. She is the second female senator from Washington, after Patty Murray.