Mary Beth Cahill is an American political advisor who served as the campaign manager of the John Kerry 2004 presidential campaign. She was Kerry's second campaign manager, replacing Jim Jordan in November 2003, after Jordan was fired by Kerry. In February 2018, Cahill was named interim CEO of the Democratic National Committee.

The 2004 presidential campaign of John Kerry, the longtime U.S. senator from Massachusetts, began when he formed an exploratory committee on December 1, 2002. On September 2, 2003, he formally announced his candidacy for the Democratic nomination. After beating John Edwards, Howard Dean, Wesley Clark, and other candidates in the primaries, he became the Democratic nominee, challenging Republican incumbent George W. Bush in the general election. Kerry selected Edwards as his running mate.