Kennedy was born in Melbourne, and grew up in Canberra, Townsville, and Perth, with his family finally settling in Northampton, a small country town north of Geraldton, Western Australia.

[6] With Northampton falling into the recruitment zone of the Perth-based East Fremantle Football Club, Kennedy made his senior (WAFL) debut during the 2005 season, finishing with six goals from six games.

However, on 11 October, it was announced that he had agreed to instead return to his native state and play for the West Coast Eagles,[9] thus enabling Carlton to secure the services of top midfielder Chris Judd in a trade.

[10] After playing in struggling teams at the start of his career—four of Kennedy's first six seasons resulted in bottom two finishes, including two wooden spoons, one each at Carlton and West Coast, respectively—Kennedy made his first finals appearance in 2011.

But with the Eagles losing their last three games by an average margin of 71 points and Kennedy being goalless in each of them, he lost his chance of winning the medal.

After Darren Glass retired midway through the season, Kennedy was named acting co-captain of the club for the remainder of 2014, along with four other players.

At the end of the home-and-away season, Kennedy finished with 75 goals and became the second West Coast player to win the Coleman Medal.

On 29 April 2018, Kennedy became West Coast's all-time leading goalkicker, overtaking Sumich with his 515th goal for the Eagles during the Western Derby.

[14] In July 2022, Kennedy kicked his 700th goal for West Coast against Carlton, and a month later he announced his retirement from the AFL.

Despite Adelaide winning by 16 points, Kennedy recorded an 8-goal haul and was chaired off to a standing ovation and a guard of honour by both teams.

West Coast Eagles Kennedy married long-time girlfriend Lauren Atkinson, an artist, in October 2016.