A one-time lobbyist, Leslie first ran for the California State Assembly in 1984, losing to Democratic incumbent Jean Moorhead Duffy by just 1 percent. With Moorhead Duffy not seeking re-election in 1986, Leslie comfortably won election to the Sacramento area 5th District over Jack Dugan, an assistant state Attorney General. He won re-election in 1988 and 1990 without serious opposition. In 1991, Leslie ran for the California State Senate in a special election for the 1st district left vacant when GOP incumbent John Doolittle was elected to Congress. He easily won re-election in 1992 and 1996.[3]
In 2000, when term limits prevented him from seeking re-election to the State Senate, Leslie ran successfully for the 4th District in the State Assembly again and won re-election in 2002 and 2004.[3]