The World Cup will be expanded to host 48 teams, up from 32, FIFA has decided.
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 sport's world governing body voted unanimously in favour of the change at a meeting in Zurich on Tuesday.
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 powerful European clubs, who objected to reform because of a crowded international schedule.
FIFA President Gianni Infantino has been behind the move, saying the World Cup has to be "more inclusive".
Speaking at a sports conference in Dubai in December, Infantino said expansion would also benefit "the development of football all over the world".
He added: "There is nothing bigger in terms of boosting football in a country than participating in a World Cup."
Despite saying "the decision should not just be financially driven", Infantino did highlight the possible financial upsides.
According to FIFA's own research, revenue is predicted to increase to $5.29bn for a 48-team tournament, giving a potential profit rise of $521m.