Garfield, the lovable fat orange cat, has gotten himself into a spot of trouble. His pal and center of abuse, the yellow dog Odie, has gone and disappeared somewhere. Their owner, Jon, is too lazy to go look for Odie himself, so he has Garfield go out and look for him. And so Garfield heads off, out into the world.

A Week of Garfield is a side-scrolling platform game based on the comic strip by Jim Davis. Garfield heads to the right through various indoor and outdoor city environments, dealing with endless vermin like frogs, birds, and mice using his judo kick skills and several different weapons such as bones that can be thrown. He has a life bar that can quickly deplete if he isn't careful, but hidden all around each stage are various items, which can replenish his health, refill his weapon supplies, and give him super speed or invincibility; be careful, though, as sometimes he'll also find fish bones which will harm Garfield if eaten.

The game is divided into seven stages, each representing a day of the week, and each with several sections. At the end of each section is a door, and Garfield must find the key hidden somewhere on the screen to unlock the door and continue. At the last door of each stage, there is a boss that must be defeated before Garfield can find the key. Each stage also has a strict time limit to keep him from dawdling, and between stages, Jon will appear to encourage Garfield or give him some advice.