An Australian international and New South Wales State of Origin representative centre or winger, he previously played in the NRL for the Canberra Raiders and the Sydney Roosters.

He missed much of the 2006 season after injuring his knee in a trail match against the St George Dragons then suffering later hamstring injuries during the year.

[9] He made his test début on the wing for Australia's opening game of the RLWC against New Zealand at the Sydney Football Stadium on Sunday, 26 October 2008.

[11] His decision to leave the Raiders came after a photograph of him simulating a lewd act with a dog during Mad Monday celebrations was published on Twitter.

[13] On 3 December 2010 it was announced that English Super League club Warrington Wolves had signed Monaghan on a one-year contract.

[20][17] Monaghan was selected to play for the Warrington Wolves on the wing in the 2013 Super League Grand final and scored the opening try in their loss against the Wigan Warriors at Old Trafford.