Before he turned 21, McCarthy invested $5,000 he had won in the state lottery to start his own deli, which he named Kevin O's. He sold it in 1987.
In 1989, McCarthy graduated from California State University in Bakersfield, where he was chair of the California Young Republicans.
McCarthy began interning in 1987 in the district office of Rep. Bill Thomas, then chairman of the Ways and Means Committee, and eventually became Thomas's district director.
McCarthy earned an M.B.A. from California State University in 1994.
In 2002, McCarthy was elected to the California State Assembly and became minority leader during his first term. While in the legislature, McCarthy served on the transition team for Gov.-elect Arnold Schwarzenegger.
In 2006, McCarthy handily won the congressional seat left open by the retirement of Bill Thomas. Since McCarthy faced little competition in the election, he donated much of the $1 million he had raised to Republican candidates across the country. GOP leaders selected McCarthy to represent the freshmen on the Republican Steering Committee.
In 2009, McCarthy was appointed chief deputy whip.