Chadian former rebel leader Mahamat Nour Abdelkerim has become the country's minister of defence.
The former enemies signed a peace pact in December in Libya
The announcement comes two months after he agreed to end his uprising against President Idriss Deby.
Mr Nour headed the United Front for Democratic Change which led a raid on the capital, N'Djamena, in April last year in which hundreds of people died.
He signed a peace deal in Libya, but other rebels in the east, which borders Sudan's Darfur region, did not.
The crisis in Darfur has spilled over the border and the governments of Chad and Sudan accuse each other of supporting the other's rebels.
As a result eastern Chad is plagued with insecurity and in the past year some 120,000 Chadians have fled their homes to join more than 200,000 Sudanese refugees already living in camps.
Last month, Chad's rejected a United Nations military peacekeeping force for its border with Sudan.
The UN has proposed a 11,000-strong force to be backed up by helicopter gunships to protect refugees in Chad and the Central African Republic displaced by Darfur's conflict.
President Deby, a former coup leader, won a third term in presidential elections in May 2006.