The jury came back with its verdict after close to three-and-a-half days of deliberation.
Rittenhouse, 18, could have been handed life in prison if found guilty of the most serious charge against him.
He was charged with homicide, attempted homicide and recklessly endangering safety for killing two men and wounding a third with an AR-style semi-automatic rifle in Kenosha.
The shootings took place during a night of protests over police violence against black people in the tumultuous summer of 2020.
Rittenhouse was 17 when he went from his home in Antioch, Illinois, to Kenosha after businesses in the city were ransacked and burned over the shooting of a black man, Jacob Blake, by a white police officer.
Carrying a weapon that authorities said was illegally purchased for the underage Rittenhouse, he joined other armed citizens in what he said was an effort to protect property and provide medical aid.
Bystander and drone video captured most of the frenzied chain of events that followed: Rittenhouse killed Joseph Rosenbaum, 36, then shot protester Anthony Huber, 26 - and also wounded demonstrator Gaige Grosskreutz, now 28.
Prosecutors portrayed Rittenhouse as a "wannabe soldier" who had gone looking for trouble that night and was responsible for creating a dangerous situation in the first place by pointing his rifle at demonstrators.
But Rittenhouse testified: "I didn't do anything wrong. I defended myself."
Breaking into sobs at one point, he told the jury he opened fire after Mr Rosenbaum chased him and made a grab for his gun. He said he was afraid his rifle was going to be wrestled away and used to kill him.
Mr Huber was then killed after hitting Rittenhouse in the head or neck with a skateboard, and Mr Grosskreutz was shot after pointing a gun of his own at Rittenhouse.
While some Americans condemned Rittenhouse as a vigilante, some on the right hailed him as a hero who exercised his Second Amendment gun rights and tried to put a stop to lawlessness.
Then-president Donald Trump said it appeared Rittenhouse had been "very violently attacked".