Under California's non-partisan blanket primary law, all candidates appear on the same ballot, regardless of party.

The candidate filing deadline was March 8, 2018, and the primary election was held on June 5, 2018.

However, Feinstein ran for re-election to her fifth full term, winning 44.2% of the vote in the top-two primary; she faced Democratic challenger Kevin de León in the general election, who won 12.1% of the primary vote.

Breifly, during the early stages of the primary, Patrick Little, a Neo-Nazi running as a Republican polled at 18% which at the time put him in second place and the likely runoff candidate against Feinstein, however, his campaign collapsed after the media reported on his views.

with Feinstein, de León, and Tom Steyer with Feinstein, de León, and John Cox The race had an undervote of around 1.3 million votes compared to the gubernatorial election, likely by Republican voters choosing neither candidate.

[186] Feinstein won 38 of the 53 congressional districts, with the remaining 15 going to De León, including seven held by Republicans.