John Kirkby kicked off his gruelling fundraising bid in a drizzly Edinburgh on November 8 and crossed the finishing line of his final marathon in Auckland, New Zealand, on Saturday.
The 50-year-old trained for 18 months and was accompanied by support runners Paul Cribb and Martin Cowles for the incredible feat.
The aim of the run was to raise awareness of people struggling to get by in the economic downturn and raise funds to support CAP's debt counselling work.
Since Kirkby started CAP in his bedroom 15 years ago, has grown to 190 centres around the UK, with plans to have 500 in operation by 2015.
The 15 marathons have raised £1.2m and will be used to expand CAP's services to areas where there is currently no CAP centre.
Kirkby said of the challenge: "It was one of those things that seemed a good idea at the time. I honestly didn't realise what it was going to require from us when we set out on this but I am overwhelmed at everyone's generosity and encouragement."
In addition to around five hours of running each day, Kirkby talked to the media for an hour every day and held fundraising dinners in the evening before travelling to the next destination and doing it all again.
"We were left with just a few hours sleep between destinations which made it pretty relentless," he said.
"We got off the plane into Australia, changed into our running gear in the airport rest rooms and ran in the dark with head torches on to the next checkpoint."
CAP now also operates in Australia and New Zealand. Some of the people who had received help from the charity turned out to cheer the runners on.
He said: "Our biggest motivation as we went round was meeting clients from all these different places who had already felt the fruit of our work. We had them in mind as we went along and it made it easier.
"We just want to know that more people like them will get the help they so desperately need."
Watch Kirkby's video blogs at www.cap15.org
