After Durban led the club to two successive relegations, leaving them in the old Fourth Division, he was sacked and Mullen was appointed caretaker manager until the end of the season.

Mullen was replaced by Frank Burrows in the summer of 1986 and he then moved on to near-neighbours Newport County, where he would end his playing days.

On 28 March 1989 Mullen was asked to take charge of Blackpool for the last eleven games of the season after the departure of Sam Ellis.

In light of Ellis' success and popularity at Bloomfield Road, Mullen only lasted eleven months before being replaced by Graham Carr.

After another unsuccessful 1995–96 season, Mullen was given the sack by the Burnley board and subsequently had short spells scouting for the likes of Bolton Wanderers and Wrexham.

The position was made permanent the following month,[6] but on 10 January 2009 he was sacked as manager following a run of four wins in sixteen games.