Sweden advanced to football's biggest stage for the first time since 2006 with a composed 0-0 draw at San Siro which completed a famous 1-0 aggregate victory in the play-offs.
Jakob Johansson's first leg goal proved the difference over 180 minutes as Lindelof stood tall to help shut out the highly-fancied Azzurri.
The 23-year-old, who has at times come under fire for his performances at club level this season, paid tribute to Sweden's togetherness.
"It is the first time I have qualified for a World Cup and I am so, so happy," Lindelof said.
"We knew coming here would be difficult but following the first game at home we believed we could do it.
"We work very, very hard. I don't know how to describe this team, we work so hard for each other. We know what we can do.
"We always believed we would go to a World Cup and here we are."
Russia 2018 will be Sweden's 12th appearance at the tournament, having reached the Round of 16 in each of their past two efforts.