A Queensland State of Origin representative hooker, he played his club football in the NRL for the Parramatta Eels, New Zealand Warriors and Brisbane Broncos.

Named after his uncle, Peter John Marsh, who was killed in a car accident before PJ was born, he attended and played rugby league for St. Brendan's College, Yeppoon.

[6] In an interview with The Daily Telegraph in 2022, Marsh recalled hearing a couple of cracking noises during the tackle, then feeling an intense pain throughout his entire body as he attempted to play the ball, stating: "It scared the absolute shit out of me.

[6] After playing five games in 2009, Marsh suffered a back injury which ultimately led to him retiring on medical grounds in March 2010, with the Brisbane Broncos paying out the final year of his contract in full.

[6][11][12] Because of his experience, Marsh is advocating for a crackdown on dangerous tackles in rugby league by having stronger penalties and deterrents including more sin binning and suspensions.

[6] Marsh said he remembers thinking crusher tackles were a "load of shit" when he first witnessed them come into the game, describing them as "worse than a punch", and said $1000 fines were a meaningless deterrent to highly paid athletes and wants players to be punished with suspensions instead.

[6] Unable to hold back their ambitions of being like their father, Marsh's wife Kelly registered their children to play rugby league while he was out of town.

[6] Marsh's eldest son Braelan played in the Under-16s boys team in the Queensland Rugby League's Cyril Connell Challenge in 2022 and was signed to the Dolphins Academy.

[13] Marsh's daughter Waverley played for The Highlanders at Murri Rugby League Carnival in 2021 where she scored nine tries and was named in the Queensland Merit team.

[15] In 2022, Marsh's youngest son Jay was a member of the Yeppoon Seagulls Under 14's team competing in the Junior Rocky Rustlers rugby league competition.