The FIFA Council agreed unanimously to the move Tuesday, with the new format starting in 2026.
FIFA made the announcement on Twitter w
ith further details expected to be published later. Since 1998, when the World Cup expanded to accommodate 32 teams, the format has stayed the same.
This latest tweak would pull in close to an extra $1bn in revenue, according to FIFA estimates.
The last World Cup in Brazil was estimated to have cost the host country $11 billion, according to its sports ministry, with FIFA covering operational costs which it says ran to $2 billion.
How will it work?
The addition of 16 more teams will mean groups are reduced from four to three sides, with swifter progression to the knockout stages.
Each nation will play the others in its group once, with the top two progressing to an enlarged knockout round comprising 32 teams. The number of games will rise from 64 to 80 but the competition will remain at 32 days in length.
It also guarantees each team will have at least two matches -- Infantino's initial plan envisaged a playoff round before the main group stage to eliminate 16 teams. Currently, the World Cup involves eight groups of four, with the top two going through the last 16 knockout round.
Infantino told reporters after the announcement: "The good news is that this format can be played in exactly the same number of days, 32, that the team winning the tournament will play a max of seven games, and that the tournament takes place in 12 stadiums."
On the possibility that three-team groups might give rise to teams conspiring to produce a result that sees both go through, the FIFA president suggested drawn games could be settle by penalty shootouts or that rankings could be used to determine qualifiers if some nations finish with identical records.
He added that the make up of the extra 16 slots would be discussed at further FIFA Council meetings.
Who will it benefit?
The smaller nations and those on the fringes of qualification for one of the world's showpiece sporting occasions.
FIFA said the motion was carried "unanimously," while Infantino had spoken at a conference in Dubai last month of confederations being "overwhelmingly" in favor.
Federations from Africa and Asia are especially keen, as they make up 110 of FIFA's 211 members, but are traditionally under represented at the World Cup.
The allocation of the new slots will be discussed after the plans have been ratified by FIFA's congress.
Infantino said after the verdict: "The upside is 16 more countries, some which would never have dreamed of playing in the World Cup, will be able to participate and others will be able to dream of playing in it.
"We're in the 21st century and we have to shape the World Cup for the 21st century. We have to look at football as more than just Europe and South America.
"Football fever in a country that qualifies is the biggest promotional tool for football that you can have. From November when you qualify to June when it takes place, these nine months are the most important."
Who is for and against?
FIFA found an ally just before the council meeting in Jose Mourinho, one of the world's most successful managers, currently at English Premier League club Manchester United, who said he was "totally in favor."
The Portuguese said though there would be 16 more matches in the competition, by virtue of more nations being involved, the fact that no additional demands would be placed on players was a key factor in his support.
Teams who reached the semifinals in 2026 would still play seven matches, like those who made the last four in 2014.
Mourinho, who has won titles in Portugal, England, Spain and Italy, told FIFA's website: "The expansion means that the World Cup will be even more of an incredible social event. More countries, more investment in different countries in infrastructure, in youth football."
The plan does have its detractors though.
Germany voiced its opposition shortly before the vote, its soccer federation chief Reinhard Grindel saying expansion could dilute the quality of football and overburden players. And Europe's top clubs agree.
The European Club Association (ECA) which represents them, released a statement shortly after the decision was made public questioning the need to deviate from the current "perfect" formula.
It called the move a political decision and said it was curious as to the urgency with which it was made given the changes won't come into effect for nine years.
In response Infantino said: "There is a dialogue open with the ECA for many years. There are some critical voices from some clubs but I prefer to focus on the positive ones.
"There are a lot who favor this decision. We have of course discussed this topic several times with the clubs. The main point was always not to add to the calendar and the burden of the players."