Newlyweds John and Jenny Grogan (Owen Wilson and Jennifer Aniston) ponder the life-changing decision to start a family. Unsure of his preparedness for raising children, John confesses his fears to his friend and fellow journalist Sebastian, who comes up with the perfect solution: John should get Jenny a puppy.
Then came Marley.
The Grogans adopt the cute, twelve pound yellow Labrador, who in no time at all, grows into a 100-pound steamroller of unbridled energy that turns the Grogan home into a disaster area. However, through the years and the mayhem, Marley sees the Grogans through the myriad challenges of a growing family. As John and Jenny come to realize, Marley - "the world's worst dog" - somehow brings out the best in them.