The 65-year-old Democrat is resigning from her House seat to become president of the Woodrow Wilson International Center for Scholars in Washington, D.C.
Harman was first elected to the U.S. House of Representatives in 1992. Harman represents a Democratic-safe district that includes several beachfront communities in suburban Los Angeles such as Venice Beach and Redondo Beach.
The governor will have two weeks to call a special election to fill Harman's seat.
Los Angeles City Councilwoman Janice Hahn has already thrown her hat into the ring, along with Secretary of State Debra Bowen.