Elected to the Newport-Mesa Unified School DistrictBoard of Education in 1964, she was reelected to the board in 1968, 1972, and 1976. In 1978, Bergeson won 74% of the vote to be elected as California State Assemblywoman for the 74th Assembly District. In 1980, she won 74% of the vote in a three-way race to be re-elected to her seat. In 1982, she again won 74% of the vote for re-election after her district was renumbered as the 70th Assembly District after the 1980s redistricting.
Bergeson made history in 1984 by becoming the first woman to have won election as both a California state assemblymember and state senator after she won 74% of the vote to be elected as California state senator for the 37th Senate District. Bergeson was re-elected in 1988 with 71% of the vote in a three-way race.
In 1990, Bergeson ran for Lieutenant Governor of California. The winner of the 1990 election for lieutenant governor was poised to make history, as Bergeson would have been the first woman to be lieutenant governor while incumbentLeo T. McCarthy would have been the first lieutenant governor to win a third term. Bergeson was unable to unseat the incumbent McCarthy, losing by a margin of 51%-42%.
Bergeson was elected to her third term as a state senator in 1992, winning 62.2% of the vote in a three-way race in her district after it was partially redrawn and renumbered the 35th District in the 1990s redistricting.
In 1994, Bergeson won more than 98% of the vote to win the election as an Orange County supervisor, representing the 5th District.