A Merseyside native, Mullin had spells in the youth systems of both Liverpool and Everton. Having been released from both Liverpool giants, Paul was invited to join the Huddersfield Town academy in 2012.
Impressing during his time there, he was signed as a professional at the Terriers in 2013, although he did not make a first team appearance for the Yorkshire club. Indeed, a short loan at Vauxhall Motors yielded 4 Conference North appearances to give a young Mullin his first taste of competitive football.
In 2014, Paul joined League Two Morecambe after a successful trial.
An initial short-term contract saw him score 3 goals in his first 7 matches and such was his impact, he signed a 3-year deal at the Globe Arena. Paul became a crucial player for Morecambe, a virtual ever-present over his 3 seasons with the Club.
After 140 appearances and 28 goals for the Shrimps, Mullin transferred to League Two rivals Swindon Town for an undisclosed fee. Again, Mullin became a key component of the side, representing the Robins 47 times and scoring 10 goals in all competitions during 2017-18.
Upon promotion, Micky Mellon brought Mulling back to Merseyside, paying an undisclosed fee for the player and signing him to a 2-year deal. For his age, Mullin brought a wealth of EFL experience to the Club, having notched close to 200 senior appearances prior to his arrival.
This experience was vital to the Club, Mullin scoring 7 goals in 29 appearances in all competitions. He was named on the bench as Tranmere won the 2018-19 League Two Play-off Final against Newport County to secure a second successive promotion.
Interesting Fact: Despite joining Rovers at just 23 years old, Paul arrived at Prenton Park having played 46, 47, 47 and 47 matches respectively in the 4 preceding seasons — all at League Two level or in associated cup competitions.