MacIntosh was born in Merionethshire. He was educated at Repton School in Derbyshire,[2] and studied linguistics at the University of Edinburgh. While at university, he was actively involved in the Edinburgh University Theatre Company and The Improverts.[3]
MacIntosh's big break in television came when he was cast as deadpan accountant Keith Bishop in The Office. He has also appeared on various shows such as Miranda and Little Britain. He formed a double act with Tim FitzHigham and they performed at the Edinburgh Fringe Festival in 2007. In 2009, be appeared alongside several other celebrities in a charity music video for the Chris Rea song "Driving Home for Christmas".

In 2010, he had a cameo role in the controversial "A Serbian Film" appearing in stock footage alongside The Office co-star Mackenzie Crook.[4] In early 2013, he prepared to play at a new West End show Geek! A New Musical at the Tristan Bates Theatre, which opened on 22 April 2013.[5] He was also a regular on the radio sitcom Cabin Pressure as Carl, the bored ATC operator. In 2013 he appeared in a national TV advert for ao.com. A year later he appeared as Barry the window cleaner in the film The Confusion of Tongues (2014).

In 2017, MacIntosh appeared as Lionel in British romantic comedy film Finding Fatimah.[6]

He appeared on Week 2 (Cheshire) of Celebrity Come Dine with Me in 2020, alongside Charlotte Crosby, Dawn Ward, Steven Arnold, and Jay Hutton.

In 2013, MacIntosh was signed on with Salopian Films for the lead part in a six-part series, For the Love of Ella, which was subsequently cancelled. It was to also star Lucy Drive, Alex Reid, Bobby Ball, Daniel Peacock, Melanie Sykes, Darren Day, Francoise Pascal and Billy Pearce. The script was written by Simon W. Golding (co-producer) and the pilot directed by James Farina (co-producer).[7]

MacIntosh also presented various music programmes on Now 80s and Now 90s.

In 2022, he made a cameo appearance in the third and final series of After Life.