The 34-year-old left Ouessant, off the west coast of France, on November 4 and raced eastwards around the globe to finish in 42 days, 16 hours, 40 minutes and 35 seconds.
Sailing the 30-meter (98 feet) trimaran MACIF, Gabart shattered compatriot Thomas Colville's 2016 record
by more than six days.
Gabart's time for the 27,859-mile voyage makes it the second fastest circumnavigation ever, behind Francis Joyon and his five-man crew aboard the giant trimaran IDEC Sport, who clocked 40 days 23 hours on January 2017.
Gabart enjoyed favorable weather conditions throughout and crossed the finish line between Ouessant and Lizard Point off England's southwest coast at about 01:45 a.m Sunday.
"I never dreamed of a time like this," Gabart told reporters after docking in the French port of Brest.
"On paper, with the weather and with what I am capable of doing with this boat, it was possible to beat the record, but in the best scenarios only by one or two days. It's quite extraordinary."
Colville, in turn, shaved more than eight days off Joyon's 2008 solo mark.
Before that, Britain's Ellen MacArthur held the record with a time of 71 days, still the fastest by a woman.
The fastest time for sailing solo around the world in a monohull is 74 days three hours 35 minutes, set by Frenchman Armel Le Cleac'h in winning the 2016-2017 Vendee Globe.
Long distance offshore sailing, both crewed and solo, has a long tradition in France.
MacArthur is the only non-French sailor to have held the solo record since American Dodge Morgan reduced the monohull mark to 150 days in 1986.