In 2009, Tom Allen appeared on Channel 4's weekly TNT Show, writing and presenting Dictionary Corner. He also appeared on Law of the Playground for the same broadcaster.
For the BBC, he has appeared in the series Sensitive Skin and The Cut, as well as biopics of Fanny Cradock (Fear of Fanny) and Frankie Howerd (Rather You Than Me). In 2008, Allen made his own documentary about identity for E4, titled Who Is Tom Allen?.
In August 2015 and March 2016, Allen appeared on 8 Out of 10 Cats Does Countdown as a Dictionary Corner guest. In October 2016, he appeared as a guest on BBC2's The Great British Bake Off: An Extra Slice, and in January 2017, he made his debut on Live at the Apollo in an episode hosted by Sarah Millican. The following month, he appeared as a panellist on the CBBC show The Dog Ate My Homework. In July 2017, he appeared on a celebrity special version of gameshow The Crystal Maze and – an hour later the same night – on Mock the Week.
He has also appeared on Big Brother's Big Mouth and Big Brother's Little Brother.
In 2018, Allen appeared on the BBC One comedy quiz show Ready or Not. He currently co-hosts Bake Off: The Professionals with former contestant from The Great British Bake Off Liam Charles, and joined the 2018 series of The Great British Bake Off: An Extra Slice as a regular contributor.
In 2019 it was announced that he would become the new host from Series 15 of The Apprentice: You're Fired!, taking over from Rhod Gilbert. Allen also appeared in an episode of Josh Widdicombe's show Hypothetical.
2020 saw Allen compete on Richard Osman's House of Games, alongside Chizzy Akudolu, Charlie Higson, and Kate Williams. He also made two appearances on QI in the same year, and appeared again on Hypothetical.
In December 2020, Allen co hosted The Great Christmas Bake Off alongside Matt Lucas as a replacement for Noel Fielding due to his paternity leave following the birth of his second child.
Allen has co-written and recorded two series of The Correspondent for BBC Radio 4. In 2009, he made guest appearances on Loose Ends and The Richard Bacon Show.
He took the lead role of young Pip Bin in the BBC Radio 4 comedy Bleak Expectations, which has so far run to five series (2007, 2008, 2009, 2010 and 2012), co-starring with Anthony Stewart Head and Richard Johnson.
In 2008, he recorded a radio adaptation of The Wooden Overcoat with Julia Davis and David Tennant, written by Mark Gatiss.
Allen has also guested as a panellist on BBC Radio 4's Just a Minute, in August 2015 and February 2017.
Allen portrayed Oliver Harper, the travelling companion of the First Doctor and Steven Taylor during a limited three-story arc in the Big Finish Productions audio dramas based on the Doctor Who series. His character is a city trader from 1966, who joined the First Doctor and Taylor in the audio plays The Perpetual Bond, The Cold Equations and The First Wave. Harper was the first ongoing companion created for the Companion Chronicles range.
Since October 2015, Allen has co-hosted the podcast Like Minded Friends with comedian Suzi Ruffell. He also guested on Ruffell's other podcast, Out with Suzi Ruffell.