Katherine Marlea Clark (born July 17, 1963) is an American lawyer and politician who has served as House Minority Whip since 2023 and is currently in her seventh term as the U.S. representative for Massachusetts's 5th congressional district, having held the post since 2013. She previously served as Assistant Speaker from 2021 to 2023 and Vice Chair of the House Democratic Caucus from 2019 to 2021. Clark was a member of the Massachusetts House of Representatives from 2008 to 2011 and the Massachusetts Senate from 2011 to 2013.

Born in Connecticut, Clark worked as an attorney in several states before moving to Massachusetts in 1995, where she worked in state government. She joined the Melrose School Committee in 2002, becoming committee chair in 2005. She was first elected to the state legislature in 2008, and contributed to legislation regarding criminal justice, education, and municipal pensions. She won the 2013 special election for the U.S. House of Representatives to succeed Ed Markey in the 5th district, and sits on the House Appropriations Committee.

Clark's district includes many of Boston's northern and western satellite cities and suburbs, such as Medford, Framingham, Woburn, Waltham, and her home city of Revere.

Katherine Marlea Clark was born on July 17, 1963, in New Haven, Connecticut. She attended St. Lawrence University, Cornell Law School, and Harvard's John F. Kennedy School of Government. She studied in Nagoya, Japan, in 1983.

In her early career, she worked as an attorney in Chicago. She then moved to Colorado, where she worked as a clerk for Judge Alfred A. Arraj of the United States District Court for the District of Colorado and later as a staff attorney for the Colorado District Attorneys' Council. She moved to Massachusetts in 1995 and became general counsel for the state Office of Child Care Services.

In 2001, Clark moved to Melrose, where she was elected to the Melrose School Committee, taking her seat in January 2002. She first ran for the Massachusetts Senate in 2004 and lost to Republican incumbent Richard Tisei. In January 2005, she was unanimously elected chairwoman of the Melrose School Committee. In 2006, she ran for the 32nd Middlesex seat in the Massachusetts House of Representatives when incumbent Mike Festa began a run for Middlesex district attorney but withdrew after he dropped out of the race.

Clark was appointed co-chair of Victory 2006, the state Democratic Party's campaign and fundraising effort for the 2006 gubernatorial election. She spent some time as chief of policy and government relations in the Massachusetts Attorney General's office.

Festa resigned his state House seat in October 2007 to become secretary of elder affairs in the Deval Patrick administration, and Clark entered the special election to succeed him. During the campaign, she emphasized her experience as an attorney and made "developing stability in state aid" her top policy issue. She won the Democratic primary in January with 65% of the vote, defeating two other Melrose Democrats. She defeated Republican real estate businessman Mark B. Hutchison, 63% to 37%. In November 2008, she was reelected to a full term unopposed.