PC Simon Harwood, 45, has been cleared of the manslaughter of Ian Tomlinson during the G20 protests in 2009.
Harwood said he used reasonable force when he hit 47-year-old Mr Tomlinson with a baton and shoved him to the ground as he walked away from police lines in the City of London.
Mr Tomlinson was an alcoholic and had slept rough for a number of years.
Giving evidence during the trial, the police officer admitted he was "wrong" to hit and push the father-of-nine, but said he did not realise that at the time.
He told the jury: "Now I've seen all the evidence and I know how poorly Mr Tomlinson was I'm sorry that I got involved, I shouldn't have hit him with a baton and pushed him."
Harwood also said he believed Mr Tomlinson, who was drunk at the time, was being deliberately obstructive and that his use of force was reasonable.
Had Mr Harwood been convicted, it would have been the first time a police officer had been successfully prosecuted for manslaughter while on duty.