Andrew Garrison was a realtor in Asherton. Later, he saves Marcus after he is captured and locked in a basement by the Sheriff and his deputies. He claims that he is FBI investigating the corrupt instances going on in Asherton (unofficially). He believes it goes all the way to the President.
He is the one who finds the tracking chip in Marcus's shoes. The two then go to Maggie after Lewis admits that Maggie has been helping him. The two find her apartment empty and the body of Alexi in the bakery.
They head to the bar, finding it on fire. Marcus instructs Andrew to help the people at the Asherton Tap while he goes to the school.
When they rejoin, they go to a motel. Andrew betrays Marcus and Maggie, and locks them in the truck of the car to turn them over to the Sheriff after knocking Marcus out. They meet the Sheriff on a lonely road, where Garrison is shot and thrown into an open grave.
After Marcus is told about the Shepherd Organization, Andrew Garrison is found to be alive. Marcus punches the man, but they seem to make up with Andrew becoming part of Marcus's cell.
Garrison once had a wife and daughter. It is currently unknown what happened to them.