The Gulf state has been heavily criticised for its human rights record and for not recognising same-sex marriage or civil partnerships.
The build-up to the tournament, which starts later this month, has also been marred by allegations that migrant workers in Qatar have been poorly treated.
Blatter was president of world football's governing body when the 2022 finals were controversially awarded to Qatar in 2010.
The 86-year-old told Swiss newspaper Tages-Anzeiger: "The choice of Qatar was a mistake.
"At the time, we actually agreed in the (FIFA) Executive Committee that Russia should get the 2018 World Cup and the USA that of 2022.
"It would have been a gesture of peace if the two long-standing political opponents had hosted the World Cup one after the other."
Blatter said he had voted for the United States and that former UEFA president Michel Platini had helped turn the vote in Qatar's favour.
"Thanks to the four votes of Platini and his (UEFA) team, the World Cup went to Qatar rather than the United States. It's the truth."
When asked why he was opposed to Qatar hosting the finals, Blatter said: "It's too small a country. Football and the World Cup are too big for that."
Blatter said FIFA had responded to widespread accusations that Qatar had mistreated migrant workers, who helped build the World Cup stadiums and infrastructure, when he was still president.
"When discussions about the conditions on the construction sites in Qatar arose after the award, we in FIFA supplemented the rules in 2012," he said.
"Since then, social criteria and human rights have been taken into account in the award process. That was late, too late. But we did it."
Blatter stepped down from his role as FIFA president in 2015 amid allegations he had sanctioned an illegal payment of £1.6million to the then UEFA president Platini.
FIFA initially banned Blatter for eight years, reduced to six, but in March 2021 he was handed a new ban for "various violations" of the governing body's code of ethics, suspending him from football until 2028.
The PA news agency has approached FIFA for comment.