Joshua Keck Harder (born August 1, 1986) is an American politician who has served as the U.S. representative for California's 9th congressional district since 2023, after representing the 10th district from 2019 to 2023. A member of the Democratic Party, he was first elected in 2018 by defeating Republican incumbent Jeff Denham. After the 2020 redistricting, he won reelection in the newly drawn 9th district, which covers the majority of San Joaquin County and includes Stockton, Tracy, and Manteca.

Harder was born on August 1, 1986, in Turlock, California. His great-great-grandfather settled nearby in Manteca, where he started a peach farm. Harder attended Modesto High School, and during that time, he interned for then state senator Jeff Denham. He went on to attend Stanford University, earning a Bachelor of Arts degree in 2008. He later obtained a joint Master of Business Administration and Master of Public Policy from the Harvard Business School and the John F. Kennedy School of Government.

In 2014, Bessemer Venture Partners hired Harder in its New York office. He moved to San Francisco two years later and became a vice president of the company. In 2017, Harder left Bessemer to campaign full-time. He moved back to Turlock and also taught business at Modesto Junior College.

In May 2017, Harder announced his candidacy, joining three other Democrats to challenge Republican Jeff Denham, who had represented California's 10th congressional district since 2013 and represented the 19th district from 2011 to 2013. As a result of California's top-two primary system, Denham and Harder advanced to the general election, with Denham taking 37.5% of the primary vote and Harder 16.7%.

California's 10th district was included on the list of Republican-held seats being targeted by the Democratic Congressional Campaign Committee in 2018. On election night and for days after the election, Denham led in the reported results. On November 9, Harder pulled ahead as absentee ballots were counted. Days later, news outlets projected Harder's victory, and on November 14, Denham conceded.

Harder ran for reelection in 2020, finishing first in the top-two open primary with 44% of the vote. He bested Republican opponents Ted Howze and Bob Elliott. Harder and Howze advanced to the general election on November 3, which Harder won with 55.2% of the vote to Howze's 44.8%. In 2020, former president Barack Obama endorsed Harder.

Following redistricting, Harder defeated San Joaquin County Supervisor Tom Patti, a Republican, with 56% of the vote in California's 9th congressional district.

In the 2024 general election, Harder defeated Republican Kevin Lincoln with 51.8% of the vote, or approximately 9,000 votes.