The 34-year-old sailor comfortably beat the previous record set by compatriot Thomas Coville last year by six days and 10 hours.
Gabart becomes just the fourth title-holder for a world record of sailing the globe solo without stopping.
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.
Gabart faced good weather throughout much of the voyage, particularly during the long and arduous Pacific section, and clocked up speeds of up to 65 kilometres an hour.
Several records broken
On his 30-metre-long new generation Macif maxi-trimaran, Gabart set a number of new solo race records along the way, including the fastest navigation of the Pacific - seven days, 15 hours, 15 minutes - and the longest distance covered in 24 hours at 1,576 kilometres.
The debut record for the race was set in 2004 by Frenchman Francis Joyon who completed the odyssey in 72 days and 22 hours.
British female sailor Ellen MacArthur took to the seas a year later, racing against the clock to break that record by just a day and a half (71 days, 14 hours).
She remained undefeated until 2016 when Coville set a new record of 49 days and three hours.
Of the four solo record holders, Gabart is the only won to have also won a competitive round the world race.
Gabart first circumnavigated the world during the 2013 Vendee Globe race, which he won.