The soul legend sang at a small street concert in Cleveland just two days before Americans go to the polls and addressed residents near the busy Cuyahoga County early voting site.
He declared, "I would like you to commit to me one thing. I do a song. You go vote. Can we do that?"
Wonder then performed at a packed rally for the leader in Cincinnati and called on the 15,500-strong crowd to back Obama, declaring, "It's time for us to truly come together and make a difference."
The president thanked Wonder for his support, telling his audience, "There may be some folks who are still undecided, just decided you wanted to hear Stevie. I can't argue with that. But for those of you - or your friends or your neighbours - who are still trying to make up their minds, this is not just a choice between two candidates or two parties. It's a choice between two different visions of America."
Democrat Obama will go head-to-head with Republican rival Mitt Romney in the vote to decide who will take office in the White House for the next four years.