The midfielder made 27 appearances for Northern Ireland, scoring three goals, and played five times in the United first team.
However, after failing to make an impact on the Red Devil's midfield - which featured Paul Scholes, Roy Keane, David Beckham and Ryan Giggs at the time - he moved on to Norwich City where he became a firm fan favourite.
He is now embarking on a very different way of life and is just one year away from becoming a Catholic priest in the Dominican Order after he made his Solemn Profession last Sunday.
The 38-year-old, who meandered around the Football League after leaving Norwich, retired from football in 2008 and has been studying to become a priest since 2009.
His vocation is in stark contrast to some of the stories that marked his career as a professional footballer.
Mulryne and teammate Jeff Whitley were suspended for two Northern Ireland World Cup qualifying games in 2005 by then manager Lawrie Sanchez after breaking a curfew, and he also dated model Nicola Chapman for a time.
He made the decision to become a priest when his football career came to an end and he began doing charity work.
Although he has rarely spoken about his desire to enter the priesthood, he did talk about his faith in a video made by the Dominican Order to mark his first profession - a stage in the process of becoming a priest - in 2013.
"After the reading of the Gospel, each brother presents themselves to their provincial and he places his hands in his and makes a profession to God, to blessed Mary and to blessed Dominic," he said.
"This for me was one of the major reasons that attracted me to the religious life, to give oneself completely to God, through the profession of the Evangelical councils.
"To take him as our example and despite our weakness and our defects, trust him that he will transform us by his grace."
He is now just a year away from being ordained and will spend the next 12 months studying theology and pastoral care.