Schiff and Garvey are running in two separate elections: one for the full six-year term and the other for the remaining weeks of Feinstein's unexpired term. Schiff was well ahead in both races.
WATCH: Adam Schiff and Steve Garvey discuss top issues facing California during U.S. Senate Candidate Forum
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In a year when control of the Senate is in play, Democrats were favored to easily hold the seat in the liberal-leaning state where a Republican hasn't won a Senate race since 1988, when President Ronald Reagan was in the White House.
Still, the campaign represents a turning point in state politics, which was long dominated by Feinstein, former U.S. Sen. Barbara Boxer and other veteran Democrats. The contest also means that California won't have a woman representing it in the Senate for the first time in more than three decades.
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Schiff is a longtime member of the U.S. House of Representatives, and was first elected to the House in 2000. Garvey, a 10-time MLB All-Star, is a former Los Angeles Dodgers and San Diego Padres first baseman. More recently, he worked as a businessman and motivational speaker.
Schiff shaped his campaign around national issues including abortion rights while continuing to play a foil to Trump, calling the former president a threat to democracy. He also contrasted his years of experience in Congress - Schiff was first elected to the House in 2000 - against Garvey, a first-time candidate who positioned himself as an outsider with fresh perspective to deal with California's long-running homeless crisis, inflation and housing costs.
Garvey calls himself a "conservative moderate" who shouldn't be buttonholed into conventional political labels, an obvious pitch to independent and soft Democratic voters in a state where registered Republicans are outnumbered by Democrats nearly 2-to-1.
The race has been largely overlooked in a year when control of the Senate will turn on a handful of competitive races, including in Ohio, Michigan, Pennsylvania, Nevada and Montana.
The Republican Party has struggled in the nation's most populous state for years, though it retains pockets of strength in rural areas, the Central Valley farm belt and parts of Southern California.
Democrats hold every statewide office and dominate the Legislature and congressional delegation by commanding margins. Republicans haven't won a statewide race in the state since 2006.
Garvey aimed a final advertising push at Latinos, who make up about a quarter of likely voters in California.
Feinstein, a centrist Democrat who was elected to the Senate in 1992, died at 90 in September 2023. Laphonza Butler, a Democratic insider and former labor leader, was appointed to the seat following Feinstein's death and decided not to seek a full term this year.
The Associated Press contributed to this report.