The 34-year-old Londoner ran a total of 295km in a world record time of 24 hours 19 minutes nine seconds.
Gill finished the final marathon (42.2km) in Miami on Wednesday night, winning the women’s title in the race, which is also known as the “777 challenge”.
She won every race during the week-long challenge, except in Antarctica where she came second despite temperatures dropping as low as -35C.
The challenge saw Gill and her competitors run in Novo in Antarctica, Cape Town, Perth, Dubai, Lisbon, Cartagena in Colombia, and Miami.
"It was a crazy ambition that I wanted to do. The challenge seemed absolutely irresistible to me," she told the BBC.
"Ten years ago, I just wanted to get fit and run the London Marathon. Now, marathon running has literally taken me around the world."
Over the last decade, Gill has completed 45 marathons, including 10 London Marathons – her fastest being just two hours 58 minutes.
Fewer than 200 people have finished the challenge since Sir Ranulph Fiennes first completed the race in 2003.
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