Antonovich served nine four-year terms on the Board of Supervisors and served until 2016, when a limit of three consecutive terms imposed by voters in 2002 forced him to leave office. That year, Antonovich ran for California State Senator for the 25th District, which includes the cities of Burbank, Glendale, Pasadena, La Canada Flintridge, South Pasadena, Monrovia, Bradbury, Duarte, Glendora, San Dimas, La Verne, Claremont, Upland, Sierra Madre, the unincorporated communities of Altadena, East Pasadena, and La Crescenta-Montrose, and the Los Angeles neighborhoods of Atwater Village and Sunland-Tujunga. He lost to Democrat Anthony Portantino, 57 percent to 43 percent.