McAndrew's first task will be to encourage people who have a place in the 2006 Flora London Marathon to run with her for Cancer Research UK.
Cancer Research UK will run a PR campaign to attract marathon runners who have not already signed up to a charity to run for it with McAndrew. Places are being announced over the next two weeks.
McAndrew will support the charity in other runs including its own 10 kilometre event, the Cancer Research UK 10 series, as well as The Great North Run, although no formal agreement with the model has been signed.
McAndrew decided to become Cancer Research UK's running ambassador after her father suffered from a variant of the disease two years ago.
"Cancer Research UK is very close to my heart as my dad was diagnosed with non-Hodgkin's lymphoma two years ago -- thankfully he's now in remission. I'm delighted to be the running ambassador for the charity because it combines the two things I'm passionate about, running and raising money to fight cancer," she said.
McAndrew completed the 2005 Flora London Marathon in just three hours 10 minutes, placing her in the "elite" athlete category.
The Leeds-born model, who starred in the first series of 'I'm a Celebrity...' has also completed last year's Great North Run.
Last year more than 1,700 people ran the marathon for Cancer Research UK, raising £1.3m. This year, the charity hopes to attract more than 1,800 and raise £1.5m, which will play a vital role in the charity's research to help prevent, treat and cure cancer.
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