Germany entered the match knowing that any victory would be enough to win the section, and the world champions will now take on Mexico in the competition's second semi-final on June 29.
Chile, meanwhile, will face Portugal in the first semi-final after a 1-1 draw with Australia.
Germany's first chance of what was a largely uneventful first period came in the 21st minute when Emre Can found some space outside the Cameroon box, but his effort was always curling wide of the post.
Cameroon almost led entering the half-time break after Andre-Frank Zambo Anguissa looked to loop the ball over Germany goalkeeper Marc-Andre ter Stegen from close range, but the Barcelona stopper made a brilliant save.
It was Germany that made the breakthrough early in the second period, however, when Draxler found Kerem Demirbay in an advanced position, and the 23-year-old found the top corner with a well-placed effort.
Cameroon's hopes of a comeback suffered a major setback in the 64th minute when they lost experienced defender Ernest Mabouka to a red card for a late challenge on Can, and less than two minutes later, Germany doubled their lead as Timo Werner headed a Kimmich cross into the bottom corner.
Cameroon had one back in the 79th minute when Vincent Aboubakar's header came off the post and went in via Ter Stegen, but a third arrived for Germany just two minutes later as Werner notched his second with a smart finish.