It was in 2003 whilst playing a friendly match against Wasps that club captain Lawrence Dallaglio took notice of Johnny and recommended the dynamic flanker to his director of rugby Warren Gatland. O'Connor joined Wasps the following year.
O'Connor made 74 appearances during his four seasons with the London club. A multi-medal winner, he was involved in two Heineken Cup victories, two Premiership titles and a Powergen Cup win.
He earned his first international call-up in 2004, making his senior debut for Ireland against South Africa in the autumn internationals. He made 12 appearances for Ireland and was part of the 2006 squad which won the Triple Crown.
Aged 25, O'Connor was named the 2005 Irish Rugby Union Players Association (IRUPA) Player of the Year. A week later he was announced as one of eight Ireland players to be included in the Barbarians squad.
O'Connor returned to his native Galway in 2007 and rejoined Connacht where he has remained for the last seven seasons. Week after week he has turned in tremendous performances in the green jersey and has been an inspirational leader both on and off the pitch.
He has battled with his fair share of injuries throughout the years, including a serious neck injury sustained whilst playing for Wasps in the Powergen Cup final which saw him stretchered from the field and out of action for several months.
His hunger, determination and commitment to put his body on the line earned him the nickname Johnny 'Concrete' O'Connor.
Speaking about his decision to retire, he said: "I'm happy with this decision I've come to following 14 years playing professional rugby and my body is telling me that it's 'my time' now.
"I've enjoyed my playing career massively and it wouldn't have been possible without all the people who've supported me along the way.
"All the coaches and support staff I've worked with at both Connacht and Wasps have pushed and moulded me into the player and person that I am today.
"I'm especially grateful to Eric (Elwood) who has believed in me from the outset and, during the last three years, has been a fantastic head coach.
"I'm thankful for the wonderful friends I've made through rugby over the years. I've played with and against some fantastic people.
"It's other players' commitment and sacrifices that have helped me develop on the pitch and that sort of unity is what makes the sport of rugby so special.
"I wouldn't have been able to achieve my goals if it wasn't for the help and support of my family and friends. I'm eternally grateful to my parents and my wife Louise.
"Looking ahead to my future, I hope to remain working in the rugby industry and keep an involvement with Connacht. I have a degree in strength & conditioning and wish to apply that knowledge, along with my first hand experience, in a sports performance capacity."
Connacht head coach Eric Elwood spoke about his former team-mate, stating: "It is with great regret that I have to bid farewell to a Connacht legend on the announcement of his retirement at the end of the season.
"Johnny is a very proud Connacht man and I know how much playing for his province meant to him. His loyalty, dedication and commitment to his province has been first class .
"He played the game hard and his willingness to push his body to the limits for his team-mates and province will be my stand-out memory of Johnny and that is why he is held in such high regard by all his team-mates and our supporters.
"I have known Johnny for over 20 years as a fellow player and as his coach and I know how hard he has worked to achieve what he did in his career.
"It came as no surprise to me that Johnny went on to be successful and win great honours in the game and play for Ireland.
"He is a great role model and inspiration to our young players in our province. When Johnny pulled on that green shirt and took to the field, you knew that he was going to give you nothing less than 100%.
"People like Johnny are winners and I hope that he stays in the game in some capacity as I believe he has a lot to offer.
"On behalf of myself, the management and supporters I thank him sincerely for everything he has done for Connacht Rugby and I would like to wish Johnny, Louise and Jack every success in the future."
Connacht Caps: 145
Connacht Points: 55