Stepanek's attorney John Bruzek said his client was influenced by social media and political rhetoric characterizing the protesters as dangerous criminals. Stepanek initially believed he was legally justified but has come to see he was wrong and apologized, Bruzek said.
"Michael understands how his conduct could have resulted in a much more serious and harmful situation," he said.
The Johnson County Attorney's Office, which agreed to Stepanek's plea deal, could face accusations of double standards as it continues to pursue charges against some Black Lives Matter protesters involved in the demonstrations last summer.
Prosecutors are pursuing 15 counts, including nine felonies, against a protest leader charged with shining a laser beam light in police officers' eyes in August.
A 20-year-old Black protester who carried an assault rifle through an Iowa City crowd in June has been indicted on a federal charge of illegally possessing a gun while using marijuana. The man, who faces up to 10 years in prison, had already been prosecuted by Johnson County on related charges after the gun was found during a traffic stop following the protest.
Separately in Des Moines, prosecutors are pursuing felony leak charges against two protesters accused of stealing an intelligence bulletin from an officer and giving it to a television reporter.
Stepanek's violence came during a downtown Iowa City protest organized by the Iowa Freedom Riders, whose members have been pushing for changes to policing for months. Police fired tear gas on them in June, outraging city leaders.
Police say Stepanek became enraged when he was stopped behind other vehicles after protesters blocked an intersection. He honked his horn then made a U-turn, squealing his tires to turn around.
Then, he shut off his lights, drove around the block, and turned onto a downtown street where there were no vehicles between him and the protesters, police say. Video shows his car striking multiple protesters, dragging one on his hood, before speeding off.
A 21-year-old protest organizer said she had a sore leg after she was mowed down and that the incident opened her eyes to the "hatred of people in this community."
"It was extremely jarring to have some stranger take it upon himself to punish a group of young unarmed people for inconvenience and/or political dissidence," the University of Iowa student wrote in a victim impact statement. She said the crime made her wary of cars and "paranoid about violence."
A police officer on the scene saw Stepanek speeding away and noted his license plate but did not pursue him, citing traffic congestion. The officer claimed to have not seen him plow through the crowd.
The Iowa City Police Department announced an investigation the next day, after video of the incident spread on social media and protesters accused police of failing to respond.
The department asked those who were struck to come forward, but only one did. Stepanek was arrested and spent 76 days in jail.