The 25-year-old has made 80 league appearances for the Championship side since joining from Chesterfield in August 2014.
Cooper is the second player to extend his stay at Elland Road this week after full-back Gaetano Berardi signed a new three-year deal on Tuesday.
Thomas Christiansen's side have started the season with wins over Bolton in the league and Port Vale in the EFL Cup.
Leeds United defender Liam Cooper has signed a new four-year deal.