Andy Mulliner started his career as a reserve player at Port Vale, though he never made a first team appearance for the club or indeed in the Football League. Despite this, in 1988 he won a cap for the Wales under-18 side in a match against Northern Ireland.

After leaving Port Vale, he joined Telford United, appearing once on Boxing Day 1989 in a 3–1 victory at Aggborough. At the start of the 1990–91 season he joined Bangor City playing in the Northern Premier League before dropping down a division to join Accrington Stanley. The following season he joined Curzon Ashton, before joining Llansantffraid in January 1992, who were playing in the Cymru Alliance.

He later played for Llandsantffraid in the Welsh Premier League, making 213 first team appearances but later spent time with many other clubs in that division. He played for Aberystwyth on loan in 1994, Rhyl in 1999, Bangor City (1999-2000), Connah's Quay Nomands (2000), Bangor City (2000), Aberystwyth (2001), Newtown (2001), Connah's Quay Nomands (2001), Caersws (2001-08), Welshpool Town (2008-09), Ellesmere Rangers (2009-10), Bangor City (2010), Ellesmere Rangers (2010-11) and Airbus UK (2011-12).

Mulliner served as assistant manager and player-goalkeeping coach at Ellesmere Rangers from 2009 to 2011. He has also worked as a goalkeeper coach at the Wolverhampton Wanderers academy (2006 to 2012), at Kidderminster Harriers (2006 to 2012), Shrewsbury Town (2006 to 2008) Shrewsbury School (2008 to 2012), Shrewsbury Sixth Form College (2007 to 2014), The New Saints (2010 to 2012), Bury (2011), Port Vale (2011) and Stockport County (2011 to 2012). He was appointed as the Head of Academy goalkeeping at Birmingham City in June 2012, and worked with the Wales under-19 squad v Germany in September 2012.

In July 2014 he was appointed Lead Academy Goalkeeping Coach at Norwich City.

In July 2015, he moved to Manchester City to become their Lead Goalkeeping Coach and passed his UEFA Goalkeeping A coaching certificate at the beginning of August 2015.