Glenn Ford, 64, had been on death row since August 1988.
He had been found guilty of killing 56-year-old Isadore Rozeman, a jeweller for whom Mr Ford occasionally worked.
US media reports say that he is one of the longest-serving death row inmates in modern US history to be exonerated.
Mr Ford had always denied killing Mr Rozeman.
Asked by a reporter how he was feeling as he left the high security prison in Angola, Louisiana, Mr Ford said: "My mind is going in all kinds of directions but it feels good."
He said that he did harbour some resentment because he had been locked up for almost 30 years "for something I didn't do" and had lost years of his life.
"Thirty years, 30 years of my life if not all of it. I can't go back and do anything that I should've been doing when I was 35, 38 and 40 - stuff like that. My son when I left was a baby, now they're grown men with babies."
State District Judge Ramona Emanuel on Monday overturned Mr Ford's conviction and sentence because of new information that supported his claim that he was not present or involved in Mr Rozeman's death, Mr Ford's lawyers said.
He was convicted over the 1983 killing and sentenced to death.
"We are very pleased to see Glenn Ford finally exonerated, and we are particularly grateful that the prosecution and the court moved ahead so decisively to set Mr Ford free," a statement by the freed man's lawyers said.
They said that his trial had been "compromised by inexperienced counsel and by the unconstitutional suppression of evidence, including information from an informant".
They also drew attention to what they said was a suppressed police report related to the time of the crime and evidence involving the murder weapon.
The family of the murder victim have also welcomed his release, US media has reported.
The many flaws in the case against Mr Ford have been listed by the US press:
There are 83 men and two women serving death sentences in Louisiana.
State law entitles those who have served time but are later exonerated to receive compensation.
It sets out payments of $25,000 (Â£15,000) per year of wrongful incarceration up to a maximum of $250,000 (Â£150,000), plus up to $80,000 (Â£48,000) for loss of "life opportunities".
A man who spent more than 25 years on death row in the US state of Louisiana has walked free from prison after his murder conviction for the 1983 killing of a jeweller was overturned.