Mulryne began his career as a youth team player at Manchester United in 1994. He was in the FA Youth Cup winning team of 1995, and became a Northern Ireland international even before he made his first team debut. His full international debut came in February 1997 against Belgium but Mulryne had to wait until the following October to make his debut for United against Ipswich in the Coca-Cola Cup. Despite being capable as a striker, midfielder or right winger, these positions were virtually monopolised by accomplished players such as David Beckham, Nicky Butt, Paul Scholes, Andy Cole and Ole Gunnar Solskjaer, and so Mulryne only managed a handful of first-team games in five seasons at Old Trafford. His only league appearance for United came on the last day of the 1997–98 season, in which he played the full 90 minutes against Barnsley. Mulryne joined Norwich City for £500,000 on 25 March 1999 in the hope of gaining more first-team opportunities. Mulryne made a promising start to his Norwich career, scoring an excellent free-kick in a televised 1–0 win at Grimsby Town in Division One which was just his second appearance for Norwich. However, a broken leg sustained in a tackle with Blackburn Rovers'Christian Dailly shortly after the start of the following season ruled him out for most of the 1999–2000 campaign. In the 2001–02 season, Mulryne was a member of the Norwich team that reached the final of the Division One play-offs. The match ended 1–1 after extra time and Mulryne missed one of the spot-kicks in the subsequent shoot-out as Birmingham City won 4–2 on penalties. Mulryne had missed another penalty earlier that season in a league match against Gillingham at Carrow Road, however Norwich won that game 2–1. Mulryne's contract was expiring that summer and there was speculation regarding his future until he signed a new three-year contract with Norwich. He was part of the Norwich side that won promotion to the Premier League as Division One champions in 2004, but they stayed there for only one season before being relegated. Mulryne then departed from Carrow Road, cancelling his contract by mutual agreement shortly before it expired. He signed for Cardiff City two months later. On 30 August 2005, Mulryne was ejected from Northern Ireland's squad by manager Lawrie Sanchez for a breach of discipline. He had made 27 appearances for the team, a highlight being a headed equaliser against Denmark in 2001. At the end of the 2005–06 season, Mulryne was released from his contract at Ninian Park having made only a handful of substitute appearances, and was not until January 2007 before he found a new club after spells having trials with amongst others, Ipswich Town, Brighton & Hove Albion, Polish champions Legia Warsaw and Barnsley. Manager Martin Ling signed Mulryne for Leyton Orient on 23 January 2007 on a free transfer after impressing on a trial. He made his debut against Brighton & Hove Albion in a 4–1 home defeat on 13 February after 16 months without first team action. He was released at the end of the 2006–07 season, having helped Orient avoid relegation which had looked almost certain for much of the campaign. He subsequently had a trial at Bournemouth and played in a friendly against Southampton and then came a trial with St Mirren in Scotland. On 25 October 2007 Mulryne joined King's Lynn FC on a non-contract basis. He was released by the club on 1 January 2008. It was announced on 14 March that Mulryne was training with Cliftonville.
