He last played professionally for Irish provincial side Connacht Rugby, in the Pro12, and represented Ireland at full international level.

Duffy also plays Gaelic football, and was previously part of the wider Mayo county team.

Having joined Harlequins, Duffy made his league debut for the Premiership side in a game against Rotherham Titans on 20 September 2003.

[5] The club was relegated in the 2005–05 season, Duffy stayed with the team as they won the 2005–06 National Division One, England's second tier league.

He was named as captain for the 2011–12 season, replacing his Galwegians clubmate and fellow Ireland cap-holder John Muldoon in the role.

[8] For the 2013–14 Pro 12 and Heineken Cup, Duffy started out the season sharing the captaincy with both Muldoon and Connacht's longest serving player, Michael Swift.

[10] It was announced in April 2014 that Duffy was one of a number of senior Connacht players that would not be having their contracts renewed and that he would leave the province at the end of the season.

Duffy was one of a number of experienced players released, including the former Scotland international Dan Parks, and fellow centurion Frank Murphy.

After playing both tests against Argentina in Argentina (the first at full-back and the second at inside centre) in June 2007 and despite getting injured in a World Cup warm up game against Scotland, Duffy was the only Connacht player included in the Ireland squad for the 2007 Rugby World Cup.He toured New Zealand and Australia in 2008 and won caps against Canada and USA in 2009.

[14] Duffy trained with the county squad for the remainder of the season, but did not feature in the 2014 Championship before Mayo were knocked out by Kerry in a semi-final replay.