A free mod for Mass Effect 3, by ME3Tweaks.

This mod for the game Mass Effect 3 allows you to use an Xbox 360 controller or other game controllers that map to their corresponding input schemes in both the MP menu screens and the game with the native interface. This mod was developed to give gamers a solution to the controller issue. 

This has two versions. You can download which one you prefer or is more suitable for your needs. The first is the non-scaling one, suitable for standard PC screen sizes, while the second is the scaling one, which works better on TVs and other high-resolution displays.

This mod was designed to be the least intrusive mod possible.