Flavin was part of the Ireland side that won the Under-19 World Championship in 1998. He then went on to play for Ireland Under-21s in the 2000 World Cup and the 2001 Six Nations. He has caps for Ireland 'A' against England Saxons and Scotland 'A'.
The London-born hooker's first game for Connacht in 2006 was away to Border Reivers, which the westerners won 29-15. In November 2010, he captained the Connacht side that defeated Samoa 26-22 at the Sportsground.
Over the last seven seasons, Flavin has made 138 appearances for Connacht and touched down for 12 tries.
Speaking about his decision to hang up his boots, the 33-year-old said: "While I will miss playing rugby immensely, I'm happy to retire at this stage of my life.
"I've had a great 16 years in the professional game and I'm proud that I've played with two fantastic teams within that period.
"I am especially proud to have been involved with Connacht Rugby over the last number of years as the province has seen huge improvements.
"I'm honoured to have been associated with that change and hopefully I have contributed as much as I could. Galway has become a very special place for me, especially with my two sons Samuel and Joseph being born here.
"With a degree in Sport Science & Management Studies as well as a Level 2 IRFU Coaching qualification, I am ready for the next step in my career and I look forward to new opportunities within rugby."
He added: "I'd like to thank the coaches, management, players and supporters of both Connacht Rugby and London Irish.
"My long career in rugby wouldn't have been possible without the amazing support I have received from my wife Clare and my parents and brothers. I can't thank them enough."
Connacht head coach Eric Elwood said: "Since his arrival here in 2006, Adrian has always conducted himself in a professional manner on and off the field and is a very popular member of our squad.
"Here at Connacht Rugby, we always look to bring in good people who can add to our culture, have good values and contribute to our team.
"Over the last couple of seasons we have had our two best finishes in the RaboDirect PRO12 and it is through the hard work and commitment of people like Adrian that we have had that success.
"Through his dedication to his profession and his desire to do well it is no surprise that he has made the elite list of players who have represented Connacht over 100 times and that is something I know Adrian is very proud of.
"I would like to thank Flav for his contribution to Connacht Rugby and his friendship over the last seven years. I wish him every success in the future."
The province's assistant coach Dan McFarland added: "Adrian has been a tremendous asset to Connacht Rugby, not only through the experience he has given us on the field but also in his leadership qualities off the field.
"I have used Flav's extensive knowledge of the game for ideas and as a sounding-board consistently over the last few years and have no doubt those skills will continue to serve him well."