Harden's most notable credits include the roles of David 'Jonty' Johnston in BBC cop drama Blue Lights, Sean Rawlins in the crime drama series Unforgotten, Gregory in the final season of the comedy series Peep Show, Walter Hill in the costume drama series Titanic: Blood and Steel, Newman Noggs and the narrator in the BBC adaptation of Nicholas Nickleby, Brendan Murphy in Jimmy McGovern's 2021 prison drama Time, and an unnamed character in Star Wars: The Last Jedi.
[6] He has also provided voices for several video games, most notably as Xenophilius Lovegood in Harry Potter and the Deathly Hallows: Part I.
[11][12] In 2018, it was followed by Troubles, on the subject of male mental health, which again debuted at the Galway Film Fleadh.
In 2021, Harden appeared in Jimmy McGovern's prison drama Time as lifer, Brendan Murphy.
The role earned him praise from many, with Esquire calling this performance, "a highly-charged, emotive turn, and the Sunday Life noting it as "superb".