A federal mediator will oversee negotiations between the National Football League and the NFL Players Association beginning Friday, renewing hope that a deal might be reached before the league’s current collective bargaining agreement expires March 4. NFL owners have threatened to lock the players out if no deal is reached by that date.

Federal Mediation and Conciliation Service Director George H. Cohen said in a statement Thursday that he had held discussions with each side and offered to try to mediate a settlement. His...