Ryan won the Funny Women award in 2008. Rachel Stubbings and Sara Pascoe were runners-up.
Ryan first appeared on television as herself in episodes of the Canadian music video review show Video on Trial between season one in 2005 and her last appearance in 2008 in season three. For her comedy work, she won the 2008 Funny Women Award and was described as "the funniest new female stand-up in Britain" by a national newspaper. After relocating to the United Kingdom, she first appeared on Channel 4's 8 Out of 10 Cats in 2012. She had previously appeared in the cast of Channel 4's Campus.
On 23 February 2013, she appeared as a celebrity contestant on BBC One's Let's Dance for Comic Relief as Nicki Minaj dancing to "Starships". Ryan reached the final, and finished in fourth place. She was later featured on the Whitney Cummings Just for Laughs 2013 Gala that was taped before a live audience on 28 July 2013. She has since taken new routines to the Edinburgh Festival. In 2013, Ryan was the subject of controversy over her participation on Mock the Week in the segment "Unlikely Lines From a Cosmetics Commercial", where one of her jokes was "We don't test any of our products on animals. We use Filipino children." Filipino groups held silent protests at the BBC office to demand an apology from her.
In 2015, Ryan replaced Steve Jones as the presenter of Hair on BBC Two. Also in 2015, Ryan became a panellist for Tinie Tempah's team on Sky 1's music/comedy panel show Bring the Noise and on the ITV2 show, Safeword. In 2016, Ryan appeared on series 2 of Taskmaster. She beat Doc Brown, Joe Wilkinson, Richard Osman and Jon Richardson, to win the season.
Ryan went on a comedy tour in 2016, called Kathbum, a name her toddler sister used to call her. In February 2017, Netflix released Katherine Ryan: In Trouble, featuring her stand-up comedy live performance at the Hammersmith Apollo in London, during that tour.
She joined Jimmy Carr in 2017 to host four series of the reboot of Your Face or Mine?. In 2018, Ryan joined American comedy panel show, The Fix as a team captain. In July 2019, Netflix released her second live stand-up special, Katherine Ryan: Glitter Room. In a 2021 interview, she was accused of racism by some viewers on social media when she attempted to encourage a female Sri Lankan designer by saying "You need to really back yourself. Do you know how confident a straight white man would be right now? Think about Boris Johnson, how pleased he'd be right now." The BBC responded that such a comment was in line with reasonable expectations of Ryan's humour. In February 2023, Ryan won the Outstanding Female Comedy Entertainment Performance award at the 2023 National Comedy Awards for Backstage with Katherine Ryan.
