The 34-year-old sailor crossed a virtual finish line drawn between the island of Ushant off France's northwest tip and Lizard Point in southwest England at 0145 GMT, comfortably beating the previous record set by compatriot Thomas Coville last year by six days and 10 hours.
The race time was announced by an observer from the World Sailing Speed Council but will be subject to checks of the boat's black box and its GPS data before final confirmation.
Father-of-two Gabart becomes just the fourth title-holder for a world record of sailing the globe solo without stopping.
Since the record was first set in 2004, nearly 30 days have been shaved off.
The debut record holder was Frenchman Francis Joyon who completed the odyssey in 72 days and 22 hours.
She remained undefeated until 2016 when Coville set a new record of 49 days and three hours which many predicted would be difficult to topple.
Gabart's 30 metre (98 foot) long new generation maxi-trimaran was helped by good weather throughout much of the voyage, particularly during the long and arduous Pacific section.
He set a number of new solo race records along the way, including the fastest navigation of the Pacific (7 days, 15 hours, 15 minutes) and the longest distance covered in 24 hours (851 miles or 1,576 kilometres).
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