Matt is the son of D.J.'s retired boss Fred Harmon. He is a veterinarian, like his father and D.J., who lived in Miami, FL prior to Fuller House where he ran his own veterinary clinic. Along with D.J., he is the co-owner of Harmon-Fuller Pet Care, the newly renamed clinic his father owned before retiring.
- Matt is Steve Hale's rival as they both wish to date D.J.. However, in the Season 1 finale, D.J. tells them that she's not ready to date yet.
- In the episode "Love is in the Air," Matt's dog, Rusty can be heard interrupting his voicemail message recording.