Former Mauritanian President, Ely Ould Mohamed Vall, died on Friday of heart attack, the presidency said in a statement.
Mauritania announced a three-day mourning period.
Born in 1953 in Nouakchott, Vall was the President of Mauritania from 2005 to 2007.
In August 2005, a coup forced President Maaouya Ould Taya out of power and Vall became the leader of the ruling Military Council for Justice and Democracy.
Afterwards, Vall and the council introduced constitutional reforms and staged parliamentary and local elections which appeared free of fraud.
Until the coup, Vall was a close confidante of the toppled president and was made head of the security forces in 1987.
He was instrumental to the success of the 1984 military coup that brought Taya to power.
He contested for office again in 2009 and lost to current President Mohammed Ould Abdel Aziz, to join opposition forces.