The son of a Sicilian immigrant who could not read English, Dom Cortese read the newspaper to his father, imagining himself as the political figures he read about. Cortese grew up working in his father's fruit orchards in San Jose's Evergreen district. After graduating from Bellarmine College Preparatory, he earned a bachelor's degree in political science from the University of Santa Clara in 1954. Following his college graduation, Cortese served his country as a first lieutenant in the United States Army and was a training officer at Fort Ord during the Korean conflict.

As owners of large tracts of orchard land, the Cortese family experienced first-hand the rapid economic changes of the Santa Clara Valley. Though the family would have preferred to maintain its orchards, high taxes compelled them to either sell property or to develop it, today leaving them with only their orchards on San Felipe Road. In addition to participating in family farming operations, Dominic Cortese owned the Country Club Villa Shopping Center. Cortese and his wife, Suzanne, have five children.

Cortese decided to run for supervisor in 1968 at the last minute, turning in his papers to the registrar of voters five minutes before the filing deadline. Cortese's District 2 challenge against longtime incumbent and fellow Italian-American Sam Della Maggiore was unexpected. Cortese's youth proved to be attractive to the politically­aware baby boomer electorate. Additionally, he garnered support from the Hispanic community for his advocacy of an eastside medical clinic, which Della Maggiore strongly opposed.

His victory encouraged other candidates to challenge incumbent supervisors, eventually resulting in a significant shift of power on the board. Together with newly­elected supervisor Victor Calvo, Cortese pursued more urban/regional issues in favor of rural/agricultural ones that had previously predominated.

Cortese won two subsequent re-elections and during his tenure chaired the Board three times. He also chaired the Local Agency Formation District twice, the Santa Clara Valley Transportation District (which he was instrumental in creating) twice, and the Local Criminal Justice Planning Board created by Governor Ronald Reagan. He served as the Board's representative on the Regional Air Quality Board, the Bay Area Conservation and Development Commission, and ABAG. He was the Board's delegate to the local Economic Opportunity Commission (Federal War on Poverty). When the EOC was under threat of takeover by the Federal government, Cortese along with two other local officials founded the Economic and Social Opportunities Commission (ESO). Cortese was asked to meet with President Jimmy Carter during the 1979 oil crisis after his proposal to nationalize the oil companies was adopted by his Board and other cities and counties throughout the state.

Cortese also served on commissions relating to drug abuse, alcoholism, consumer affairs, and the status of women. Cortese was a strong voice for his many Hispanic constituents, and he named Jose Martinez as the first Mexican-American to the Santa Clara County Planning Commission. Cortese fought to upgrade the conditions of the county fairgrounds.

Although Cortese had no real ambitions to be elected to higher office, Leo McCarthy persuaded him to run for state assembly in 1980, where he served until 1996. Assemblyman Cortese served as chair of the Assembly Committee on Water, Parks and Wildlife, the Selected Committee on California Wine Production and Economy; and the Wine Industry Task Force of National Conference of State Legislatures.