Mr Biden campaigned in Pennsylvania and Ohio, as Mr Trump toured the voting battlegrounds of Wisconsin, Michigan, North Carolina and Pennsylvania.
National polls suggest a firm lead for Mr Biden in Tuesday's election.
But his lead is narrower in the handful of states that could decide the result.
More than 98 million people have already cast their ballots in early voting, putting the country on course for its highest turnout in a century.
In the US election, voters decide state-level contests rather than an overall single national one.