[1] In 2002, whilst studying for his A Levels at The Ravenscroft School, Griffin landed a job co-presenting the children's interactive TV show Smile (credited as DJ Devstar) alongside Yates, Fearne Cotton and Nev the Bear.
Griffin joined BBC Radio 1Xtra at the launch in August 2002, where he and Yates presented The Lowdown with Reg and Dev on Saturday afternoons.
Following further schedule changes in September 2005, Griffin moved to Saturday afternoons where he stayed until 2007, when he became presenter of the weekday early morning show.
[3] In September, he moved from the weekend slot to replace Greg James as host of the weekday early breakfast show, between 4am and 6:30am.
In March 2014, he left the weekday slot and returned to the weekend breakfast show, taking over from Gemma Cairney.
As of January 2022, Dev presents Heart's Evening Show from 7-10pm Monday to Thursday, replacing Mark Wright, who has moved back to weekends.
Griffin reached the final of the 2017 series of Celebrity Masterchef, alongside Ulrika Jonsson and eventual winner, Angellica Bell.
In July 2023 Griffin was the subject of an episode of Who Do You Think You Are?, where he discovered that a maternal great-uncle had participated in the Easter Rising at Dublin City Hall.