Harris, who has made 15 appearances for Great Britain, made his debut against Papua New Guinea in 1996 and also had a spell in Rugby Union, representing Wales in the 2004 Rugby Union World Cup before switching back to Rugby League with the Bulls.
Speaking of his decision, Harris said: "I?ve enjoyed my time with GB, have been very proud to play for them but now is the right time for me to retire.
?I?ve had to decide what my priority is and that is to play well for the Bulls for the next three to four years
?I felt to be able to do that to a high quality, week in, week out, something had to give and that is Great Britain.
"I?ve been lucky enough to have missed only one game for Bradford and I want to keep that consistency up while getting the quality higher.
?I?ve enjoyed it here more than anywhere and want to retire at Bradford but my main aim first is to win things, as many trophies as possible, and that?s the reason why I?m retiring for international rugby."
Commenting on the decision of Harris to retire from international Rugby League, Great Britain Head Coach Brian Noble said: "I am sorry that Iestyn will not be available for Great Britain in the future.
?He has been an important member of our squad over the last two seasons and has made a solid contribution to what we have tried to achieve. We respect his decision to retire.
"However, we have a great number of high quality players available to us and myself and the other coaches are completely confident that the overall strength of the squad will not be adversely affected.
"We would like to wish Iestyn all the best for the remainder of his career.?Like