"The FIFA Council unanimously decided on a 48-team #WorldCup as of 2026: 16 groups of 3 teams," FIFA tweeted after the voting.
The tournament will have an initial stage of 16 groups of three teams. Two teams from each group will qualify for a Round-of-32 knockout stage.
World football governing body FIFA's governing panel voted unanimously in favour of the change here on Tuesday.
The number of matches in the tournament will go up to 80, from the existing 64. But the eventual winners will still play seven matches to claim the trophy, the same number as a 32-team World Cup.
FIFA President Gianni Infantino mooted the idea of a 48-team World Cup last year.
He has previously advised the governing body to introduce penalty shoot-outs in group matches that end in a draw to stop teams from plotting a favourable result for both sides.
The 37-member FIFA governing body also had an option of voting for a 40-team tournament, with 10 groups of four or eight groups of five, but favoured the 48-team proposal.
European places at the competition will likely rise from 13 to 16. Africa and Asia could have as many as nine teams each.
At the 2014 World Cup in Brazil they had five and four teams respectively. FIFA could decide by May how many entries each continent has.
The other major decision regarding 2026 - who will host the event - is not scheduled for consideration until 2020 with a bid featuring the United States, either on its own or in conjunction with one or both of Canada and Mexico, an early favourite.
Increased revenue for FIFA due to more teams could be a driving force behind the expansion of its flagship tournament.
FIFA's research has suggested that an expanded tournament would rake in an additional 632 million dollars profit on the current format, with the tournament revenue increasing to 6.42 billion dollars.
Infantino's expansion plans have been criticised heavily by certain quarters but received backing from the likes of English Premier League club Manchester United's head coach Jose Mourinho and Argentina legend Diego Maradona.