Olsen will succeed Connie Conway of Tulare after the November election, when Conway's term ends.
Olsen, 40, is vice chairwoman of the Assembly education and agriculture committees. She has been involved in education reforms, including the implementation of a new school-funding formula and a law streamlining teacher dismissals.
She rises as Republicans are fighting to overturn the Democratic supermajority in the Assembly, which has left the GOP with limited influence. The party is trying to broaden its appeal to minorities and independents, causing tensions among state Republicans over stances on social issues and immigration.
"We all have the same goals of lowering taxes, creating great good-paying stable jobs and revitalizing our schools in California," Olsen said about unifying Republicans.
Olsen was first elected in 2010 after serving on the Modesto City Council from 2005 to 2009. She also directed marketing and communications for California State University, Stanislaus.
The Assembly became the first California legislative body led by women when Speaker Toni Atkins, D-San Diego, was sworn in May.
The Senate is also getting a new leader. Los Angeles Democrat Kevin De Leon becomes president pro tempore in October.