Walsh attended Christ's Hospital before going on to read Art History at Cambridge University, which she described as 'the most boring three years of my life". After graduating she worked in various small art galleries in East London.
While working in galleries, Walsh attended comedy writing evening classes including Stand up and Deliver and as a direct result wrote for Jo Caulfield on BBC Radio 4. In 2006 she switched to comedy full-time. In 2007 Walsh was approached by Frank Skinner to appear in a TV pilot, Frank Skinner's Skateboarding Dog for Avalon Entertainment.
Walsh was runner-up in AmusedMoose LaughOff 2006 on the Edinburgh Fringe, appeared at the Edinburgh Festival Fringe in 2007 and 2008, and appeared — between writing and filming — at Afterhours as well as co-hosting the AmusedMoose LaughOff 2009 with Jack Whitehall.
Walsh has since written for several TV and radio shows, and has made several appearances on radio and television, including Edinburgh & Beyond on the Paramount Comedy Channel, The Late Edition on BBC Four and Out to Lunch on BBC Radio 2 in 2008.
In 2009, Walsh wrote for and appeared on The Now Show on BBC Radio 4, appeared on Winging It on BBC Switch, and made videos for Current TV. Walsh is also an occasional contributor to comedy podcast Answer Me This!. In January 2009, Walsh created a comedy film night called 'Popcorn Comedy' with Jon Petrie (Brother of CBBC's Ed Petrie). In the summer of 2009 Walsh was a co-host and writer of Channel 4's TNT Show.
In August 2011, Walsh was nominated for an Edinburgh Comedy Best Newcomer Award, in recognition of her first full hour long show. She received critical acclaim for the show which drew on her life since breaking her arm in the Worthing Birdman Competition in August 2010. She has also appeared on "So Wrong It's Right", a BBC Radio Four comedy presented by Charlie Brooker.
On Mon 3 Mar 2014 18:30GMT BBC Radio 4 appeared on the comedy panel game Just a Minute and was the first person to win on a debut.
In 2008 Walsh was a stand-in continuity presenter for CBBC and for its show All Over the Place. On 12 June 2009, Walsh was a guest panellist on 8 Out of 10 Cats, on 18 August 2009 appeared on You Have Been Watching, Newswipe with Charlie Brooker, and on 3 September on Mock the Week. On 15 October, she also appeared on the third episode of the new series of Never Mind The Buzzcocks, on Noel Fielding's team. Then later on 13 September on Phill Jupitus's team along with JLS.
On 15 August 2010, Walsh injured herself with a suspected dislocated shoulder and fractured arm after leaping from a pier during the annual Worthing International Birdman festival. On 8 October 2010, she appeared on 8 out of 10 cats still with her arm in a sling, saying that she had 4 inches of metal in her arm.
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