A US appeals court on Tuesday granted a new hearing for Kris Maharaj, 78, who has been jailed for more than 30 years for a 1986 double murder in Miami.
The ruling means that Maharaj's lawyers will be able to present new evidence which they say proves the two men were killed by members of a drug cartel.
His lawyer claims a Colombian hit man killed Derrick and Duane Moo Young.
Maharaj's lawyer, Clive Stafford Smith from human-rights organisation Reprieve, applauded the decision, saying "it is a great day for Kris, and I hope now we will finally get him the justice he has long been denied".
But a spokesman for the Miami-Dade State Attorney's office, Ed Griffith, told BBC News: "We stand by the outcome of the very lengthy and fair evidentiary hearing that Maharaj received in the state court, where the judge found these witnesses and/or claims to not be credible or have any merit."
The defence team plans to present new evidence from six cartel associates to argue that the two men, who were business partners of Maharaj, were killed after members of Pablo Escobar's Medellin drugs cartel caught them embezzling laundered drug money.
The new ruling from the Eleventh Circuit Court of Appeals in Atlanta says "new evidence" would demonstrate that Maharaj could not have been found guilty of the Moo Young murders "beyond a reasonable doubt".
The judgment adds that the statements by the witnesses, which include Escobar's preferred hit man John Jairo "Popeye" Velasque, "independently corroborate one another".
They will also present evidence that one hotel guest on the night of the murders, Jaime Vallejo Mejia, was a member of the drug cartel.
The former businessman, who has been in poor health, had been on death row for 15 years but had his sentence commuted to life imprisonment in 2002.
A British man will have a chance to win his freedom after more than 30 years in a Florida jail.