After another colts premiership with Norths in 2000, Griffin joined the coaching staff of the NRL's Melbourne Storm and was Chris Anderson's then Mark Murray's assistant in 2001 and 2002.
He was appointed as assistant to head coach Ivan Henjak for the 2010 NRL season, in which the Broncos failed to make the finals series for the first time since 1991.
[7] Less than three weeks from the beginning of the 2011 NRL season, Griffin became the third ever coach of the Broncos when he was unexpectedly announced to be replacing Henjak.
Griffin employed a policy of resting key players such as Darren Lockyer and Sam Thaiday after mid-season representative matches and Brisbane's ladder position slipped.
However without injured captain Darren Lockyer, Brisbane were knocked out of contention by eventual premiers, the Manly-Warringah Sea Eagles.
On 21 October 2015, it was announced that Griffin had accepted the head coaching position with the Penrith Panthers on a three-year deal.
[8] On 4 October 2017, Griffin signed a new two-year extension to stay as Penrith coach until the end of 2020 after guiding the club to consecutive finals appearances.
Griffin told the media "We were officially on top of the ladder, having overcome this huge run of injuries earlier in the year, but nothing.
He was granted a two-year contract to begin in 2021, with a third year in the club's favour, following the sacking of Paul McGregor earlier in the 2020 NRL season.