A 2-1 win at Croatia on the strength of Romelu Lukaku's brace has seen Marc Wilmots' side become the third European team to guarantee a spot in Brazil.
With a game to spare, Marc Wilmots' men triumphed over the Balkan side thanks to two first-half strikes from Everton forward Romelu Lukaku, ensuring that Niko Kranjcar's 83rd-minute goal did not take away three points from the visitors.
The victory means that the Rode Duivels sit top of Group A in UEFA qualification with 25 points - eight above second-place Croatia, which also only has one game left to play.
Fellow Group A competitor Serbia has an outside chance of claiming a playoff spot, though Scotland, Macedonia and Wales cannot reach the tournament in Brazil.
The World Cup 2014 hosts have already been joined in next summer's competition by Japan, Australia, Iran, South Korea, Netherlands, Italy, United States, Costa Rica and Argentina.
Belgium is in prime position to claim one of eight World Cup seeds, which will be awarded to Brazil and the additional top seven qualified teams in the FIFA World Ranking released Thursday. Belgium was ranked sixth in the September ranking.