Mullen has been acting since he was four but only professionally since he got his role on And Mack. He also works in local theater productions. He has said that it has been his dream since he was young to be on Disney Channel.
He wrote, produced, directed, and starred in short film, Me, My Phone, and I (2018), which was featured in the 2018 Santa Barbara Shorts program.
Mullen resides in Santa Barbara, California and attends Oak Park Independent School in Oak Park. He has a younger brother, Aidan Mullen.