John Grogan (OW) is a reporter. He gets lucky and marries Jennifer (JA) who is a columnist and doing better than him and much more famous, and is also quite beautiful. Stress starts building up in their relationship and they are not yet ready for a baby. Sebastian (ED), Grogan's friend suggest they should get a dog. And, so it is.

They get for them a Labarador and name him Marley. But as it turns out Marley is not like normal dogs. He has a lot more energy, eats a lot more, and causes a lot more trouble. And he has a weakness, thunder. No one is ready to take care of him because of his exceptionally destructive nature. Grogan's career picks up as he gets promoted to a columnist and starts writing about his life with Marley. The rest of the movie is about how Marley goes on to become the most loved and unforgettable member of the family.