Demonstrators gathered in central Cleveland and west side neighbourhoods after the acquittal of patrolman Michael Brelo, 31.
In a written verdict delivered to a packed courtroom, the judge said Mr Brelo’s actions in the November 2012 shootings were justified because he believed that someone in the car containing Timothy Russell and Malissa Williams fired shots at police at the beginning, middle and end of the chase.
Mr Brelo remains on unpaid suspension while officials consider administrative charges against him.
The officer put his head in his hands as the judge issued the verdict that was followed by angry protests, with some holding a mock funeral, carrying signs asking: “Will I be next?”
The city of Cleveland earlier agreed to pay the families of Mr Russell and Ms Williams a total of three million dollars (£1.9m) to settle a federal civil rights action.
The acquittal came at a time of nationwide tension over the deaths of black suspects at the hands of white officers, and following a determination by the US Department of Justice that Cleveland police had a history of using excessive force and violating civil rights.
“In many American places, people are angry with, mistrusting and fearful of the police,” Cuyahoga County common pleas judge John O’Donnell said.
But he said he would not “sacrifice” Mr Brelo to an angry public if the evidence did not merit conviction.
Mr Brelo, who fired 49 shots, including 15 through the windscreen while standing on the bonnet of the suspects’ vehicle, would have faced as many as 22 years in prison had the judge convicted him on two counts of voluntary manslaughter.
The deaths occurred after Timothy Russell’s car backfired outside police headquarters on 29 November 2012. Thirteen officers fired at the car with Mr Russell and Ms Williams inside after a 22-mile chase involving 62 marked and unmarked cars and reaching 100mph.
Mr Russell, 43, and Ms Williams, 30, were each shot more than 20 times. Mr Brelo was the only officer charged because prosecutors said he waited until the pair was no longer a threat to fire his final 15 rounds.
Prosecutors argued they were alive until Mr Brelo’s final shots, but medical examiners for both sides said they could not determine the order in which the deadly shots were fired.
Mr Russell’s sister Michelle said she believed Mr Brelo would ultimately face justice.
“He’s not going to dodge this just because he was acquitted,” she said. “God will have the final say.”
Authorities never learned why Mr Russell did not stop the car. He had a criminal record including convictions for receiving stolen property and robbery.