Constable David Brown, 30, broke down after the jury of 10 women and five men returned the not guilty verdict at the High Court in Glasgow yesterday.
He had been accused of causing the death of 65-year-old John Lacon by crashing his police van into Mr Lacon's Fiat Doblo in Glasgow last year.
Temporary judge John Beckett, QC, told Mr Brown: "The jury has found you not guilty, you are free to go."
The officer, who is now working in police intelligence, said: "Thank you my lord," before leaving the court and hugging his family.
However, the victim's family said the outcome had left them with a sense of injustice. They added: "The court process has been a harrowing experience for all members of the family.
"We have been disgusted at the conduct of Strathclyde Police throughout this process.
"The process has been exhausting and we have no more energy left to give it. We have been destroyed and nothing can change that."
It emerged yesterday the officer had wanted to plead to a reduced charge of causing the death by careless driving, but this was rejected by the Crown.
The jury could also have convicted him of this reduced charge.
The court heard Constable Brown was responding to three "officers in danger" emergency calls after a riot broke out at Kelvingrove Park during the celebrations surrounding the wedding of the Duke and Duchess of Cambridge on April 29 2011.
Mr Lacon sustained serious head injuries in the crash and died in the city's Western Infirmary 12 days later.
Mr Brown admitted he made an error of judgment but said he only had a split second in which to react.
The court heard traffic lights on Great Western Road at the junction of Dorchester Avenue were red as Mr Brown approached, but he decided it was safe and carried on. Mr Lacon, of Scotstoun, Glasgow, who had the green lights and was turning from Dorchester Avenue into Great Western Road when his taxi was struck by Mr Brown's vehicle. The constable said he thought Mr Lacon's taxi was slowing down.
Mr Lacon's son-in-law, Paul Dyer, 44, was in the taxi at the time of the crash.
He said: "I saw the police car and I called out to John, but he didn't even have time to brake."
The family had to make the heartbreaking decision to switch off Mr Lacon's life support.
Constable Brown told the court he made a mistake in going through the junction and said he now has to live with the consequences. He added: "What I am going through is nothing compared to the suffering of the family of Mr Lacon."
The court heard the officer in danger call, which all police are trained to respond to immediately came after trouble flared in the park.
Mr Brown said that as he approached the junction of Great Western Road with Dorchester Avenue the traffic lights were at red and he slowed down from about 40 to 50mph to between 10 and 20 mph.
The officer said: "I slowed down and checked my speed.
"There was a white taxi coming down. I looked at it and was clear in my mind the taxi's seen me and he's slowed down. I would say he was doing about 10mph when I saw the taxi slowing. I thought it was going to slow just because of the way it came out. His side had the green light.
"There was no reason for him to be going slow unless he had seen me. I thought he had seen me and was going to stop, but then his speed increased."
Constable Brown said he immediately braked when he realised the taxi was coming through the junction.
A Strathclyde Police spokesman said: "We deeply regret the loss of life and our sympathies are with Mr Lacon's family. It would be inappropriate however, to comment on a decision which has been taken by a jury as part of the judicial process."