1. Dempsie se narodil v Liverpoolu v 1987, ale vyrostl v západní Bridgford v Nottinghamu. He received his acting training from the Central Junior Television Workshop, Nottingham.
2. He has been the voice of the Clearasil advertisements in the UK. Dempsie is a keen Nottingham Forest football fan and attends many home and away matches, he appeared on the UK Saturday morning football show Soccer AM wearing a Nottingham Forest football shirt.
3. In November 2008, he appeared in The Moment of Truth, episode 10 of the BBC show Merlin.
4. In 2010 he voiced Steven, a gay teenager from Nottinghamshire in the Radio 4 play Once Upon a Time. As of 2015, he has appeared in the first three of its five seasons and it is unknown if he will come back.
5. He has also appeared in Harry & Paul on BBC Two, appearing as a northerner who was presented as a gift from the character Harry was playing to his daughter.