[4] He became well known for his role as Tyres O'Flaherty, the bicycle riding raver, in two episodes of the Channel 4 sitcom Spaced, and for his appearances at the Edinburgh Fringe and the Melbourne Comedy Festival.

[4] He played Mac, a former member of the British Army's Parachute Regiment in the 2008 horror film Outpost and as a zombie in Shaun of the Dead.

[citation needed] He has appeared in all three series of The Maltby Collection on Radio 4 as Des Wainwright, an eccentric security guard who keeps repeating himself and reminding people he was in the SAS.

In 2010, he had a major role in the film Burke & Hare alongside his Spaced co-stars Simon Pegg and Jessica Hynes.

[12] In 2020, he starred in Dead Still, a six-part Irish-Canadian television drama series, alongside Eileen O'Higgins & Kerr Logan.

[13] The series is a co-production between Ireland's Deadpan Pictures and Canada's Shaftesbury Films and is written by John Morton, and directed by Imogen Murphy and Craig David Wallace.

[14][15] In 2021, Smiley appeared in the lead role in The Toll, a Welsh black comedy film later released in the United States with the title Tollbooth.