Tiernan is a writer, comedian, podcaster, actor and tired dad. He has written for a number of animated shows including Hey Duggee, Stan and Gran and Duck and Frog amongst many others. Tiernan was a professional stand-up comedian for twenty years, performing at comedy clubs, theatres and festivals all over the world but then he sort of stopped that as he found it hard to stay up past 10pm anymore. He has also written for several well known comedians too, for TV and tour shows including several jokes on Frankie Boyle’s New World Order for BBC2.

He co-runs the Comedy Club 4 Kids, which puts on stand-up shows for children 6+ and families. The company won the Victoria Wood Edinburgh Comedy Award at the Edinburgh Fringe in 2025. Tiernan also writes and co-hosts the award winning children’s podcast Bust or Trust: A Kids’s Mystery Podcast, produced by Small Wardour. In between all that, he mostly eats crisps.