The 22-year-old leaves the Globe Arena after an undisclosed compensation fee was agreed between Swindon Towm and Morecambe.
Mullin signed a three-year-deal with the Shrimps in September 2014 after initially signing a short-term deal in the August of that year.
The forward went on to make forty-six appearances in 14/15 scoring eight goals, followed by forty-seven appearances in 15/16 netting ten goals in all competitions.
2016/17, which proved to be Mullin’s final season with the Shrimps, saw him match his goal scoring and appearance record of the previous year. After spending much of the first half of the season coming off the bench during Cole Stockton’s time at the club, Mullin enjoyed back-to-back games from January to May scoring six in throughout that period.
Morecambe Football Club would like to thank Paul for his contribution over the past three years and wishes him well for the future.