Claire Lomas was in tears but said she was "over the moon" as she completed the 26.2-mile (42.2 kilometre) course in her bionic ReWalk suit, which mimics the response that the wearer's joints would make if they were not paralysed.
Hundreds of people lined the streets and three mounted members of the Household Cavalry gave the 32-year-old a guard of honour as she finished the course on The Mall in central London.
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Lomas, a former chiropractor who was left paralysed from the chest down following a horse-riding accident five years ago, said: "There were times when I questioned whether I would make it when I was training.
"Once I started, I just took each day as it came and every step got me a step closer."
She walked about two miles a day, cheered on by her husband Dan and their 13-month-old daughter Maisie, and her parents.
Lomas will not appear in the official results and did not receive a medal when she finished as competitors have to complete the course on the day of the race to qualify for a medal.
But a dozen other runners in the race have given her their own medals in recognition of her achievement.
Lomas, who now works as a jewellery designer, raised more than £86,000 ($140,000, 107,000 euros) for a charity which funds research to develop treatments for paralysis caused by a broken back or neck.
"I have had tremendous support since my accident which I am so grateful for, some don't have that," she said.
"Some people lose the use of their arms as well. A cure needs to be found."
The £43,000 ReWalk suit, designed by Israeli entrepreneur Amit Goffer, enables people with lower-limb paralysis to stand, walk and climb stairs through motion sensors and an onboard computer system.
