Her fellow news anchor, John Suchet, will continue to present 'Five News' at 5.30pm and 7pm.
She said: "I couldn't have worked anywhere better. I've been so happy at Five and I'll miss the incredibly talented people in the newsroom but after ten years I feel it's time for a change.
"Working in TV news has been a tremendously exciting and exhilarating experience and I will miss that day to day buzz but I feel now is the right time to focus on other areas."
Young has no immediate plans other than continuing to host Radio 4's 'Desert Island Discs'. She became the new presenter of the popular radio show in June last year, replacing former host Sue Lawley.
Young caught the public's attention when she perched rather than sat behind a desk to read the first ever news bulletin on 'Five News'.
She left Five in a blaze of publicity in 1999 to join ITV News, before returning to the channel in 2002.
Chris Shaw, senior programme controller at Five, and a former editor of Five News, said: "Kirsty was the Face of 'Five News' when it launched and she defined a new style of news presentation. Obviously we're sorry she is leaving but understand that she wants a change and everyone at the channel wishes her the very best."
Lisa Opie, Five's managing director of content, said: "Kirsty has played a key role in the success of 'Five News' and I hope we will still see her appearing on the channel from time to time in the years ahead."
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