All you have to do is play a 38 match season in the England League (Premier League). Choose one of strongest teams, so either Manchester United, London FC (Chelsea), Arsenal or Merseyside Red (Liverpool). Play 5 minutes match time and beginner difficulty and it should be a walk in the park. Achievement will unlock after finishing the final game and are confirmed champions.
EDIT: It is NOT required for you to complete any cup games during the league season so they don't have to be included. (Thanks to ek I LewAy x)