Zoe Koplowitz's time of 30 hours and 10 minutes may be the slowest in the course's history but it did nothing to detract from her achievement: she has multiple sclerosis and did the entire marathon on a pair of purple crutches.
Ms Koplowitz, 50, a marathon veteran from New York, combated rain, rush- hour traffic and fatigue to complete the 26-mile course at 4pm yesterday.
Her journey to the finishing line in The Mall was not the slowest time for a women's marathon: Ms Koplowitz holds that record, with the 30 hours and 52 minutes it took her to complete last year's Boston Marathon.
A spokesman for the Multiple Sclerosis Society, which will benefit from sponsorship of Ms Koplowitz's efforts, said: "Obviously, after that length of time it has taken her to finish today, she was really feeling it. She is now resting and literally putting her feet up."
Members of the community safety group the Guardian Angels and the 100 Yeomanry Royal Artillery Regiment who escorted her along the route cheered as she finished.
Towards the end, Ms Koplowitz, who was frequently forced to stop after being plagued by painful spasms, was moving at 1mph. Heavy traffic also forced her to use the pavement, which added to her discomfort.
Ms Koplowitz has competed in 13 marathons.
More than 30,000 runners completed the race, won by the Moroccan Abdelkader El Mouaziz. The women's race was won by Kenya's Joyce Chepchumba, whose time of two hours, 23 minutes and 22 seconds earned her a pounds 78,000 bonus for a course record.