Iestyn Harris played at centre in Warrington's 10–40 defeat by Wigan in the 1994–95 Regal Trophy Final during the 1994–95 season at Alfred McAlpine Stadium, Huddersfield on Saturday 28 January 1995.

Harris played in the 2003 Rugby World Cup in Australia, where Wales lost in the quarter-finals to eventual winners, England, despite leading the game for 60 minutes.

Harris was selected in the Great Britain team to compete in the end of season 2004 Rugby League Tri-Nations tournament.

He played for the Bradford Bulls at stand-off, kicking a goal in their 2005 Super League Grand Final victory against Leeds Rhinos.

On 10 May 2006, Harris announced he would be retiring from playing international rugby league with Great Britain, just a week after being named in a 36-strong training squad for a June 2006 Test against New Zealand.

On 26 September 2006, he confirmed that he would continue to play for Wales, and was scheduled to return to the side against Scotland at the Brewery Field, Bridgend in the 2008 Rugby League World Cup qualifying match on Sunday 29 October 2006.

Harris had been linked to a player-coach role with Crusaders, but he decided to sign for National League One club Featherstone Rovers instead.

On announcement of his tenure as assistant coach to Brian Noble at Celtic Crusaders, he agreed termination of his contract at Featherstone Rovers and an immediate end to his playing career.

Appointed alongside Harris were the more experienced Kevin Ellis and Clive Griffiths, and the trio's first match was against England on 17 October, which they lost 48–12.

Wales lost by 36–0, but New Zealand were frustrated by not being able to play their attacking football full of flair, and this was due to Harris' team's good defence.

Iestyn coached Wales in the 2013 Rugby League World Cup held in their own country and fellow British nation England.

On 9 April 2014, Harris resigned from the Wales post, after taking up the head coaching role at the Super League club, the Salford Red Devils.

[14] On 14 October 2009, Harris was announced as assistant coach to Brian Noble at Wales-based Crusaders Rugby League, alongside Jon Sharp.