House Democrats on Tuesday chose Representative Robert Garcia of California to lead their party on the Oversight Committee, elevating a less experienced member over an older and more seasoned one to a key post as younger Democrats seek more influence over their party’s future.

Mr. Garcia, 47, a second-term lawmaker, emerged from a field that had initially included three other contenders in an internal contest for a position that will make him among Democrats’ most visible foils to Republicans and the Trump administration. His selection suggested a rebuke to the seniority system that Democrats have traditionally used when awarding powerful positions in Congress.

The top spot on the Oversight Committee, the main investigative panel in the House, became vacant after Representative Gerald E. Connolly of Virginia died last month at 75. The position has seen considerable turnover; Mr. Connolly was the fourth person to hold it in six years, none of them younger than 60 years old.

In the end, Mr. Garcia defeated an older and far more experienced lawmaker: Representative Stephen F. Lynch of Massachusetts, 70, who assumed Mr. Connolly’s duties after he stepped aside. His victory came after two other contenders — Representatives Kweisi Mfume of Maryland, 76, a former president of the N.A.A.C.P., and Jasmine Crockett of Texas, 44, whose fiery sparring at hearings has frequently drawn attention online — withdrew on Tuesday before the official vote.

The internal election, conducted by secret ballot, came as the Democratic Party is gripped by profound infighting over its identity in the wake of the 2024 presidential election.

Among the many battles is one over age. As the party tries to reorient itself ahead of next year’s midterm elections, many younger Democrats have been pushing for older figures in the party to cede power. Mr. Connolly’s death — which came just months after he won an election for his position against one of the most prominent young Democrats, Representative Alexandria Ocasio-Cortez of New York — further fueled that debate.