The tour headed out from Dublin towards Waterford,a ride of 192km but was decided by a sixty man bunch sprint which Cavendish won.
Having been blocked out of a medal in the Olympics, the Team Colombia rider, who had eleven stage wins this season including two in the Giro D'Italia and four stages in the Tour De France,was delighted to be back to winning ways and said: "I was very pleased with the team performance today.
"My form is not so good after just travelling back from Beijing, so it just shows how you need such a strong team behind you. You saw how well they worked today, like always. I think we have shown all year how strong we are as a team, and to come to Ireland and do that is perfect. To come away with the yellow jersey after the first stage is even better.
"You can never get tired of winning. And the feeling is obviously a bit sweeter when you are tired, too."
Cavendish finished in a time of five hours and was ahead of Garmin Chipotle's Julian Dean.David Millar was 50th whilst Magnus Backstedt who is married to Olympic Champion and daughter plus grand daughter of a Coventrian Nicole Cook, was in 25th place.
Stage two today is a 158km ride from Thurles - Loughrea.