Zimbabwe's High Court has ruled that Simon Mann can be extradited to Equatorial Guinea to face trial over a foiled coup in the West African nation.
Mann was rearrested shortly after his release from prison last year
The British ex-SAS officer was jailed in Zimbabwe on arms charges in 2004, and rearrested shortly after his release last May.
He had appealed against extradition on the basis that he might be tortured.
With his appeal turned down on Wednesday, Mann's lawyer will now file an appeal to Zimbabwe's Supreme Court.
"We are appealing the first thing tomorrow (Thursday) but we have not had full sight of the whole judgment as it was only delivered this evening," said Jonathan Samkange.
Mann, 55, was arrested when his plane, loaded with 61 alleged mercenaries and military equipment, landed at Harare airport in March 2004.
He was accused of trying to buy arms as part of a plot against Equatorial Guinea President Teodoro Obiang Nguema, and sentenced to seven years in jail.
Most of his co-accused were released from a Zimbabwean prison in 2005, and Mann himself was briefly released last year after his sentence was reduced for good behaviour.
But shortly after his release he was rearrested on an immigration warrant while awaiting deportation.
Likelihood of torture
Last May, a Harare magistrate's court agreed to a request by Equatorial Guinea that Mann be extradited to stand trial there.
His lawyers appealed against the decision on the basis Mann was likely to be tortured in Equatorial Guinea and his extradition would be tantamount to a death sentence.
Sir Mark Thatcher, son of former UK Prime Minister Margaret Thatcher, was fined and received a suspended sentence in South Africa for his involvement in the affair.
President Obiang Nguema has ruled Equatorial Guinea, a former Spanish colony, since he seized power from his uncle in a 1979 coup.