In 2000 he moved to Cumbrian side Whitehaven He accepted his first Super League head coaching role at Warrington in August 2002, replacing David Plange.
Cullen successfully steered Warrington away from relegation, by winning 2 games against Halifax and Castleford ending the season with a thumping 50–10 loss at Wakefield.,[7] and towards play-off football.
It was this success which bought Cullen an extended rein at the helm due to the loyalty of the fans despite falling short of expectations with the playing roster he had.
On 26 May 2008, following a run of poor form that culminated in a 36–28 to struggling Castleford, Cullen resigned from his position as Head Coach amid heavy pressure from fans and pundits.
[citation needed] He was the longest-serving coach in the league at the time of his departure, having spent six years in charge of the Wires and guided them to a Challenge Cup semi-final and a play-off victory.