Richard Anthony Jones from Kansas was released from jail after witnesses said they could not tell the two men apart.
A judge ruled there was no evidence to keep him in jail.
Mr Jones said finding a photo of the other man - who as well as looking like him, shares the same first name - was a "needle in a haystack moment".
'I don't believe in luck, I believe I was blessed,' Mr Jones told the Kansas City Star.
So far no criminal case has been filed against his double - known only as Ricky - who gave evidence at Mr Jones's robbery retrial and denied committing the crime.
While not saying Ricky was responsible, the judge found that based on the new evidence, no reasonable juror would have convicted Mr Jones.
Mr Jones said that he began to despair that he would ever be released from jail after repeated efforts to appeal against his 19-year conviction for a 1999 robbery.
"All my appeals had been denied. It has been a rough ride," he said.
But in 2015 he told researchers from the Midwest Innocence Project - a group that aids wrongly convicted prisoners - about a man called Ricky he had heard about. Mr Jones had been told by fellow inmates that he looked identical to Ricky.
"When I saw the picture of my double it all made sense to me," he said.
Mr Jones had been convicted based mostly on eyewitness evidence.
There was no physical, DNA or fingerprint evidence that linked him to the crime.
The researchers found that not only did the other man bear an uncanny resemblance to Mr Jones, he lived near the scene of the crime in Kansas City, Kansas, whereas Mr Jones lived across the state line in Kansas City, Missouri.
Lawyers for Mr Jones also said he was with his girlfriend and her family at the time members of the public were robbed in a park.
They argued that police identity procedures 17 years ago were deeply flawed.
A lawyer working on his case said the team were "floored by how much" Mr Jones and his double looked alike.
Mr Jones told the Kansas City Star that he was now adjusting to life outside of jail and was happy to be back with his children.
A US prisoner who spent 17 years in jail for a robbery he did not commit has spoken of his relief that researchers found his lookalike.