Gloucester-born Wayne Russell, 34, has run the equivalent of about 200 marathons since he began the charity challenge on 6 September last year.
He finished the journey in Greenwich at about 15:45 BST.
The run has raised about Â£28,600 for the Superhero Foundation, which helps families in need of medical treatments.
On completing the challenge, Mr Russell was greeted by a large crowd of friends, family and well-wishers.
He said: "I'm absolutely overwhelmed, to be honest.
"Having spent the best part of the last year alone, running into such an incredible reception was mind-blowing."
Mr Russell said the trip was inspired by the death of his sister, who died aged 35, and who "dedicated her life to charity".
"I want to thank every single person that donated, shared and supported me and my run," he added.
"We've raised more than Â£25,000 for an incredible cause, and I just can't imagine a more perfect end.
"I just hope I've made my family proud. I wish my sister could have seen this."
A man has completed a 5,000-mile (8,000km) solo run around the British coastline, during which he has slept rough and spent less than Â£3 a day.