ALGIERS - Algerian government radio said he died on Monday morning in an Algiers military hospital after a heart attack.
Gaid Salah, 79, was seen as Algeria's de facto strongman since a pro-democracy movement with his backing pushed out the country's longtime President Abdelaziz Bouteflika in April.
He played a key role pushing through the December 12 presidential elections in the face of stiff opposition on the streets.
Gaid Salah was present at the inauguration of this gas-rich country's new president last week.
The new president, Abdelmajid Tabboune, declared an exceptional full week of mourning, in an indication of Gaid Salah's importance.
President Tebboune announced that the head of land forces, General Said Chengriha, would take over as acting chief of staff of the armed forces.
The army's prominent role was underlined last week at Tebboune's inauguration, during which he embraced Gaid Salah and presented him with an order of merit immediately after his own swearing-in.
Soon after mass protests erupted earlier this year, Gaid Salah's televised speech urging President Bouteflika to quit led to the veteran leader's swift resignation.
The army then backed a series of arrests of Bouteflika allies and senior businessmen in an anti-corruption campaign that was widely seen as a purge of the military's rivals within the ruling system.
But it was not enough to appease the Algerians, many of whom had begun calling for Gaid Salah's resignation and for the military to step away from the running of the major natural gas exporter.
One constant chant throughout the protests has been for: "A civilian state, not a military state."(FA)