Reilly led The Buddies’ goalscoring charts in all competitions last season, netting 22 goals and averaging a goal every two games as he helped the side clinch the league title and return to the top tier of Scottish football.
The 25-year old has experience in playing in the Scottish Premiership, having done so with Heart of Midlothian in the 2015/16 campaign, making 28 appearances in the competition.
His career began with Queen of the South, rising through the youth ranks to make his first team debut in 2010, coming on as a substitute in a 5-1 Scottish League Cup win over Dumbarton, in which he scored the fifth goal.
The frontman would go on to make 133 appearances for his local club, whilst finding the back of the net on 42 occasions before sealing a move to top tier side Hearts.
After a loan spell at Dunfermline Athletic in the 2016/17 season, Reilly signed for fellow Championship side St Mirren, who he would help return to the Premiership last campaign.
Speaking about the signing, Manager Darrell Clarke said, “I’m delighted to bring Gavin into the club on a free transfer and he arrives on the back of a very successful campaign last season.
“He’s at an age now where he is looking for consistency and I believe we have the environment here where he can flourish.”
“Gavin adds to the options we have in attack and I’m sure that he will fit well into the squad that we have here already.”
Shortly after agreeing terms, the striker signalled his delight at finalising his move to the Memorial Stadium, “I’m happy to get everything over the line and I’m really looking forward to getting started.
“I have always had the ambition to come and play in England and felt that this was the right time to make that move. With the club being in Sky Bet League One, it was a good selling point for me and Darrell Clarke has been great so far in the times that I have spoken with him.
“I have done my research and I know that there’s a great following from Rovers fans and hopefully they will support us again in their numbers this season and we will do our best to give them something to cheer.”