Staff Sergeant Alhaji Koroma had pleaded guilty to nine charges at the court-martial before being sentenced to 30 years in prison on Monday, said Ministry of Defence spokesperson Lieutenant Colonel Issa Bangura.
The charges included "conspiracy to commit mutiny, mutiny, failure to suppress mutiny, aiding the enemy, communicating with the enemy, stealing public service or property, and conduct to the prejudice of military discipline," he added.
Koroma is the first of 27 suspected coup plotters on trial to be convicted.
On November 26, armed attackers stormed a military armory, two barracks, two prisons and two police stations, clashing with security forces.
Twenty-one people were killed and hundreds of prisoners escaped before authorities were able to regain control after what they deemed a coup attempt by members of the armed forces.
At least 80 people were arrested in connection with the clashes, most of them military personnel.
Former Sierra Leone president Ernest Bai Koroma was charged with treason and other offences for his alleged role in the coup attempt.
Koroma in January received permission from judicial authorities to travel to Nigeria for medical treatment.
His trial had been due to resume in Sierra Leone on March 27, but the former president is still in Nigeria, according to his team.