Kennelly, 27, had previously said he would return to Ireland to play Gaelic football only after his contract with the Swans was up but family reasons, as well as the toll AFL football was taking on his body, forced him to reconsider.
"I wanted to go home and play [Gaelic football]", Kennelly said on Thursday.
"If I did stay and play, I'd be half the player I was."
Kennelly said he was mindful of returning home while he was still able to play his native sport at the highest level. When quizzed further on his motivation to go back to Ireland, Kennelly's response was direct and simple.
"I grew up idolising my father," he said. Tim Kennelly, Tadhg's father, was an All-Ireland champion for Kerry. He died in 2005 due to a heart condition.
An emotional Kennelly said the decision to leave the club and the friendships he had forged there over ten years was far from easy. He said addressing the players to inform them of his decision was particularly difficult.
"It was the hardest thing I've ever done. I love a lot of those blokes in that room. After playing my first game I gave it a real crack and here I am ten years later."
Swans coach Paul Roos said there was no question of there being any disappointment at the club regarding their star defender's decision.
"There was a real concern that he wasn't going to be able to fuilfil his ambitions and make an impact [playing in Ireland]. We are absolutely conviced, and 100 per cent supportive, of his decision," said Roos.
"Based on the last two years and Tadhg's genuine concern for his body, the injury problems he has had with his groins, shoulders and knees, it has fast-tracked that decision by six months.
"We have always known that family commitments back home, and also a burning desire to play for his county Kerry and follow in the footsteps of his late father, would one day take him back."
