Born in Annapolis, Maryland, Martin has been playing guitar since he was in 6th grade when he received his first guitar for Christmas. His first band, was Overflow, where he was the singer and guitarist, started with his friend and DJ and Steve Sievers, who now helps Martin run his clothing line, LeVeL 27. Billy Martin is a vegetarian and is a huge animal lover. His middle name comes from the famous Rat Pack member Dean Martin. However, rumors still persist that he was named after the Michael Jackson song Billie Jean.

While recording GC's third album The Chronicles of Life and Death, he and Benji Madden switched guitar roles. (Madden was the original lead guitarist while Martin was the original secondary guitarist.) Martin also plays keyboards on the album, with the exception of "The Truth", and occasionally plays keyboards at their concerts. Martin, who enjoys drawing, created the artwork for The Chronicles of Life and Death album sleeve and cover. He also designed all the artwork for the videos "Predictable" and "The Chronicles of Life and Death".

He plays Paul Reed Smith (PRS) guitars, Mesa-Boogie Amps, and Boss Effect Pedals.

Billy Martin co-wrote "Mountain" and "Ghost of You" off of the Chronicles of Life and Death cd.

Martin's favourite director is Tim Burton and his favourite film is Burton's "The Nightmare Before Christmas".

Martin dislikes annoying people, lazy people, snakes, spiders, and people who don't use their blinkers.

Martin is working on a picture book with action figures.

Martin produced most of the tHrOne CD's.

Billy Martin and Benji Madden sang background-vocals in the Song "Last Train Home", for Lostprophets Album "Start Something".