Fifa president Gianni Infantino made the change one of his top priorities after replacing the disgraced Sepp Blatter in the role last year and the move was rubber-stamped during a meeting in Zurich on Tuesday.
The world's greatest football event will see another 16 teams added to the current 32, with an initial stage of 16 groups of three teams before a knock-out phase where only the bottom team in each group will miss out.
The number of matches at the tournament will rise from 64 to 80 but the eventual winner will still play seven games and, due to the constraints of the European football season, it will be staged within 32 days.
The decision to accept Infantino's plans will be seen as a triumph by the 46-year-old Swiss-born administrator, who is trying to put his mark on the job after years of controversy surrounding his predecessor's reign.
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