The decision marks a major coup for the body’s president, Gianni Infantino who has made enlarging football’s showcase event the centerpiece of his young administration.
With the new format, an initial stage of 16 groups of three teams will precede a knockout stage for the remaining 32 when the change is made for the 2026 tournament.
The number of tournament matches will rise to 80, from 64, but the eventual winners will still play only seven games.
The tournament will be completed within 32 days – a measure to appease European clubs, who objected to reform because of a crowded international schedule.
However, the next World Cup is in 2018 which will be held in Russia.