The California Democratic Party, also known as the Democratic Party of California, is the affiliate of the Democratic Party in the U.S. state of California. It is headquartered in Sacramento, the state's capitol.

With 45.27% of the state's registered voters as of February 2025, the Democratic Party has the highest number of registrants of any political party in California. It is currently the dominant party in the state, and is one of the largest affiliates of the national Democratic Party. The party currently controls the majority of California's U.S. House seats, both U.S. Senate seats, the governorship, and has supermajorities in both houses of the state legislature.^{[citation needed]}

Since the beginning of the 1850s, issues regarding slavery had effectively split the California Democratic Party. By the 1853 general election campaign, large majorities of pro-slavery Democrats from Southern California, calling themselves the Chivalry (later branded as Lecompton Democrats), threatened to divide the state in half, should the state not accept slavery. John Bigler, along with former state senator and lieutenant governor David C. Broderick from the previous McDougall Administration, formed the Free Soil Democratic faction, modeled after the federal Free Soil Party that argued against the spread of slavery.

The Democrats effectively split into two camps, with both the Chivalry and Free Soilers nominating their own candidates for the 1853 election. By 1857, the party had split into the Lecompton and Anti-Lecompton factions. Lecompton members supported the Kansas Lecompton Constitution, a document explicitly allowing slavery into the territory, while Anti-Lecompton faction members were in opposition to slavery's expansion. The violence between supporting and opposition forces led to the period known as Bleeding Kansas. Splits in the Democratic Party, as well as the power vacuum created by the collapse of the Whig Party, helped facilitate the rise of the American Party both in state and federal politics. In particular, state voters voted Know-Nothings into the California State Legislature, and elected J. Neely Johnson as governor in the 1855 general elections.

During the 1859 general elections, Lecompton Democrats voted for Milton Latham, who had briefly lived in the American South, as their nominee for governor. Anti-Lecomptons in turn selected John Currey as their nominee. The infant Republican Party, running in its first gubernatorial election, selected businessman Leland Stanford as its nominee. To make matters more complicated, during the campaign, Senator David C. Broderick, an Anti-Lecompton Democrat, was killed in a duel by slavery supporter and former state Supreme Court Justice David Terry on September 13.

Until the early 1880s, the Republican Party held the state through the power and influence of railroad men. The Democratic Party responded by taking an anti-corporate, anti freedom of attainment position. In 1894, Democrat James Budd was elected to the governorship, and the Democratic Party attempted to make good on their promises to reform the booming railroad industry. The party began working closely with the state's railroad commission to create fair rates for passengers and to eliminate monopolies the railroad companies held over the state. The main effort focused on making railroads public avenues of transportation similar to streets and roads. This measure passed and was a great victory for the Democrats, but the honeymoon would not last. Budd was to be the last Democratic governor for thirty years. The struggle between the anti-monopolists and the railroad companies was, however, a key and defining issue for the Democratic Party for some time.

Despite their relative lack of power during this period, the Democrats in California were still active in pursuing reform. The party supported fairer railroad policies and crusaded for tariff reform. The party also supported the large scale railroad strikes that sprung up statewide. The corruption of the time in both the railroad companies and the government led to a change in political dynamic. The people of the state moved away from both of the main parties and the Progressive Movement began.

While the Progressives were successful in creating positive reform and chasing out corruption, the movement drained away many of the Democratic Party's members. As their movement ended, the Republicans won the governorship, but the Democratic Party had a distinct voter advantage.