There has been ungoing uncertainty over their participation in the tournament because of the US-Israel war with Iran.
And the Iranian football federation said earlier this month it was "negotiating" with Fifa to relocate the country's World Cup matches from the US to Mexico.
"Iran will be at the World Cup," Infantino told AFP. "We're delighted because they're a very, very strong team, I'm very happy.
"The matches will be played where they are supposed to be, according to the draw."
Iran are due to face New Zealand and Belgium in Los Angeles on 15 and 21 June respectively, and Egypt in Seattle on 26 June.
The tournament, which begins on 11 June, is being hosted by the US, Canada and Mexico.
Mexican President Claudia Sheinbaum said her country was prepared to host Iran's matches if needed but Infantino, who attended Iran's 5-0 friendly win against Costa Rica in Turkey on Tuesday, insisted they would participate in the tournament as planned.
"I've seen the team, I've spoken to the players and the coach, so everything is fine," he insisted.
Mehdi Mohammad Nabi, the vice president of the Iranian Football Federation (FFIRI), added: "For us, what matters most are Fifa's rules and regulations. We will comply with whatever Fifa decides.
"Every host country has made commitments to Fifa and must honour them."
He said Infantino had come to the game in Turkey while en route from Mexico to Qatar.
"Having learned that we were organising friendly matches here, he came to see us in person, and we had a fruitful discussion," he explained.
"Given our history in this competition, it is only natural that Fifa should support the Iranian team. Mr Infantino is providing the necessary support to our national team and has given our players a great boost."
Earlier this month, US President Donald Trump said in a post on social media that Iran would be "welcome to the World Cup" before signalling he felt they should not be involved "for their own life and safety".
In response, Iran said it was the US which should forefeit their place in the tournament.
Iran's Minister of Sports and Youth Ahmad Donyamali also said his country was not in a position to participate in the tournament.
On one of the most significant dates in Fifa's calendar - when the final six nations to qualify for the 2026 World Cup will be confirmed - Fifa president Gianni Infantino was in Antalya to watch Iran's emphatic 5-0 win over Costa Rica.
That is the clearest indication yet that Iran do not intend to boycott the World Cup.
Fifa had remained notably quiet after the outbreak of war, but Infantino has now appeared to shut down any suggestion of a boycott, saying: "Iran will be at the World Cup... that's why we're here."
He also made clear that there will be no change to the schedule.
All of that may suggest there is confidence the war will be over before 15 June, when Iran are due to face New Zealand in Los Angeles.
