Cullen's work was exhibited in solo and group exhibitions both in Australia and internationally. Cullen was well-established as a Sydney "grunge" painter when he won the prestigious Archibald Prize for his portrait of actor David Wenham in 2000. In 2002 he represented Australia at the 25th São Paulo Art Biennial in 2002.
He entered the Archibald Prize at least nine times, was hung at least eight times, and won once, in 2000. He was a finalist in 1997, 1999, 2001-2004, 2006 (with his painting Edmund, depicting gallery director and art historian Edmund Capon), in 2011 and 2012.