The United Automobile Workers union will endorse President Biden on Wednesday, delivering an influential boost to a president who faces a battle against former President Donald J. Trump to win the support of labor groups, according to a person familiar with the plan.

Mr. Biden, who appeared on a picket line with striking union workers in the fall, was to provide the keynote speech at a union conference in Washington and address “the top issues facing working-class Americans,” according to a media advisory for the event.

The union was expected to announce the endorsement at the event, according to the person familiar, who spoke on the condition of anonymity to discuss the plan.

The value of the union’s endorsement to Mr. Biden may be less about persuading members to back him than in motivating them to vote. The union has estimated that only about 30 percent of its members supported Mr. Trump in 2016. But without the union’s formal backing and investments in turnout, Mr. Biden could suffer a drop-off in members who show up to vote in critical swing states like Michigan.