Kell Brook, Harry Miles, Don Broadhurst and Kerry Hope are also set to be in action.
Mr Kell, 40, from Hertfordshire, said it would take about four days to complete the distance.
Mr Kell, whose brother-in-law served in Afghanistan, is fund raising for the forces' charity Help for Heroes.
Speaking to the BBC on Friday, Lillian Kell said his whole family has been devastated by his murder.
He stepped in for No. 1 contender Kell Brook, a fellow Brit who sustained a foot injury while training.
The mother of Mr Kell has also appealed for the violence to end.
Richard Kell, 40, from Hertfordshire, made the 210-mile (338km) trip from Billericay in Essex to Barry Island in the Vale of Glamorgan.
Michelle Bachelet, Executive Director of UN Women, opened the meeting, along with Georg Kell, Executive Director of the UN Global Compact.
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Mr Kell, a bank worker, said watching re-runs of Gavin and Stacey, which was broadcast from 2007 to 2010, was helping keep his spirits up.
Richard Kell will run from Gavin's home town of Billericay in Essex to Barry Island in the Vale of Glamorgan, where Stacey and her family live.
Trevor Kell, 35, a Protestant father of three, who had just started driving a taxi, was shot dead on Hesketh Road, off the Crumlin Road in north Belfast, as he stopped to pick up a fare on Tuesday night.
The child's grandfather Kell Hutchence has launched proceedings in Australia seeking sole custody of the couple's child after concerns over a new relationship Miss Yates began while being treated at a clinic for a nervous breakdown earlier this year.
Following the murder of Mr Kell, 30-year-old father of two, Gary Moore, from the Limavady area of County Londonderry was shot dead as he worked on a building site on the mainly loyalist Monkstown estate on the outskirts of north Belfast on Wednesday afternoon.
With Kell on Earth, people have seen the fashion world in a lot of different ways and they've seen how PR works but they very rarely see the kind of access that we have and characters as unfiltered as Kelly Cutrone and the people who work for her.
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