Kirchner, 60, whose wife Cristina Fernandez de Kirchner is the country's current president, died in a hospital in the southern city of Calafate, Telam reported.
Kirchner was little known politically when elected to the presidency.
Soon after taking office in May 2003, Kirchner made the stunning move of firing powerful military and police officials and overturning amnesty laws for military officers accused of torture and assassinations under the country's military rule from 1976 to 1983.
Succeeded by his wife in October 2007, Kirchner was elected a National Deputy for Buenos Aires Province in 2009 and designated Secretary General of the Union of South American Nations in May of this year,
Kirchner, who underwent two surgical procedures this year for cardiovascular problems, reportedly died of a heart attack.