The duo will join co-star James 'Arg' Argent in running the 26 miles alongside thousands of others on Sunday, April 22.
Mucklow and Kilbey are aiming to raise £10,000 for Samaritans, and have planned a number of events to help reach the target figure.
"We know how important a service like Samaritans is, my mum has experienced depression and our friends Frankie and Joey Essex lost their mother to suicide," Kilbey said. "We want people to realise that it is okay to talk about their problems, and if they feel they can't talk to family or friends, Samaritans is there round the clock."
Mucklow added: "Cara and I are taking our training really seriously, we've been going for runs in-between filming for TOWIE and we want to make all our supporters proud. We are urging all our fans to dig-deep, sponsor us and help raise vital funds for Samaritans!"
Fans can sponsor the pair by visiting their Virgin Money Giving page.
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