The 2010 United States Senate election in Wisconsin was held on November 2, 2010. Incumbent Democratic Senator Russ Feingold lost re-election to a fourth term to Republican challenger Ron Johnson, a businessman and first-time candidate. Johnson was the first Republican to win a Senate election in Wisconsin since 1986. Feingold also became the fifth senator in a row from Wisconsin's Class 3 Senate seat to be defeated for re-election in the general election, and the seventh in a row overall to lose by a defeat in either the primary or general elections. Johnson was re-elected in 2016 in a rematch with Feingold.

Russell Dana Feingold is an American politician and lawyer who served as a United States Senator from Wisconsin from 1993 to 2011. A member of the Democratic Party, he was its nominee in the 2016 election for the same U.S. Senate seat he had previously occupied. From 1983 to 1993, he was a Wisconsin State Senator representing the 27th District.