In the process, the explosive winger, who also plays at full-back, earned the title of 'Connacht's all-time leading try scorer' with 34 tries (170 points); a record he still holds.
His pace and agility caught the attention of other clubs and Carr left the Sportsground in 2011 for a short spell with Leinster Rugby. Over the last two seasons, he has scored seven tries for Leinster in 25 starts and 8 appearances as a replacement.
Carr, aged 27, has represented Ireland at Schools, Under 19 and Under 21 level, including five games in the U21 World Championship. He has two Ireland 'A' caps, having played against Canada and England.
Speaking about his return to Connacht on a two-year contract, Fionn said:
"I'm delighted to have re-signed for Connacht. I thouroughly enjoyed my three seasons there and I can't wait to get back to the club and continue to improve my game. I can see that there is fantastic work being done at Connacht both on and off the field. I'm really looking forward to being part of that again and contributing to the growing success over the next couple of seasons."
Tom Sears, Connacht Rugby CEO said: "Everyone at Connacht is delighted to be welcoming Fionn back to the Sportsground. He enjoyed huge success here in his first spell and we are confident he will hit those heights again and make a big impact next season"
"He is a proven try scorer with the ability to do something special and he will add more quality to the hugely talented back line we have.
"Fionn's recruitment is one of several key signings we anticipate making in the coming weeks and months."