Claire Conner McCaskill (/məˈkæskəl/; born July 24, 1953) is an American politician and attorney who served as a United States senator from Missouri from 2007 to 2019. A member of the Democratic Party, she previously served as state auditor of Missouri from 1999 to 2007. As of 2025, McCaskill is the last Democrat to have represented Missouri in the U.S. Senate.

McCaskill is a native of Rolla, Missouri. She graduated from the University of Missouri and the University of Missouri School of Law. McCaskill served as a member of the Missouri House of Representatives from 1983 to 1989, as Jackson County Prosecutor from 1993 to 1998, and as the 34th State Auditor of Missouri from 1999 to 2007. She ran for governor of Missouri in the 2004 election, defeating Democratic incumbent Bob Holden in the Democratic primary and losing to Republican Matt Blunt in a close general election.

McCaskill was elected to the U.S. Senate in 2006, the first woman to be elected to the chamber from Missouri (Jean Carnahan was appointed upon the death of her husband). Re-elected in 2012, McCaskill was defeated in 2018 by Republican challenger Josh Hawley. Since February 2019, McCaskill has served as a political analyst for MSNBC and NBC. She is also the author of the memoir Plenty Ladylike (2015).

McCaskill was born in Rolla, Missouri. Her father, William Young McCaskill (1925–1993), served as a state insurance commissioner during the administration of Governor Warren E. Hearnes. Her mother, Betty Anne (née Ward; 1928–2012), was the first woman elected to the city council of Columbia, Missouri. Betty Anne McCaskill lost a race for a seat in the state House of Representatives to Leroy Blunt, the father of U.S. senator Roy Blunt and grandfather of former Missouri governor Matt Blunt.

McCaskill spent her early childhood in the small Missouri town of Houston, later moving to Lebanon, and, eventually, Columbia. She attended David H. Hickman High School in Columbia, where she was a cheerleader, Pep Club president, a member of the debate club, a musical cast member, and homecoming queen. While attending the University of Missouri, McCaskill joined Kappa Alpha Theta sorority, graduating in 1975 with a B.A. in political science. She received her Juris Doctor (J.D.) from the University of Missouri School of Law in 1978. In the summer of 1974, before graduating from the University of Missouri, McCaskill studied at the Institute on Comparative Political and Economic Systems at Georgetown University.

From the time she graduated from law school in 1978 until her exit from the U.S. Senate in January 2019, McCaskill spent all but three years of her professional career in the public sector. The exception is the three years she spent in private practice as an attorney at a Kansas City law firm (1989 to 1991). Following her graduation from law school, she spent one year as a law clerk on the Missouri Court of Appeals for the Western District, which sits in Kansas City. Thereafter, McCaskill joined the Jackson County prosecutor's office, where she specialized in arson cases.

In 1982, McCaskill was elected to represent the Brookside neighborhood of Kansas City in the Missouri House of Representatives. She left the State House and contemplated running for Jackson County Prosecutor in 1988, but did not pursue the position when her mentor, fellow Democrat and incumbent Prosecutor Albert Riederer decided to seek another term.

In 1990, McCaskill was elected to the Jackson County Legislature (the equivalent of a county commission or county council).