Told in first-person narrative, the book portrays Grogan and his family's life during the thirteen years that they lived with their dog Marley, and the relationships and lessons from this period. Marley, a yellow Labrador Retriever, is described as a high-strung, boisterous, and somewhat uncontrolled dog. He is strong, powerful, endlessly hungry, eager to be active, and often destructive of their property (but completely withoutmalice). Marley routinely fails to "get the idea" of what humans expect of him; at one point, mental illness is suggested as a plausible explanation for his behavior. His acts and behaviors are forgiven, however, since it is clear that he has a heart of gold and is merely living within his nature.

During his escapades he makes a two-minute credited appearance in the movie The Last Home Run (filmed in 1996 and released in 1998).

The strong contrast between the problems and tensions caused by his neuroses and behavior, and the undying devotion, love and trust shown towards the human family as they themselves have children and grow up to accept him for what he is, and their grief when he finally dies fromgastric dilatation volvulus (a stomach torsion condition) in old age,^[1] form the backdrop for the biographical material of the story.