The announcement of his death comes several weeks after the state-run Saudi Press Agency said Abdullah was suffering from pneumonia and had been admitted to the hospital.
King Abdullah became king of the oil-rich nation, a key U.S. ally in the Middle East, in August 2005. But he'd been running Saudi Arabia since 1996, following his half-brother King Fahd's stroke.
In the context of the kingdom's conservative circles, Abdullah was seen as reformer and often came up against the more hard-line clerics.
Since ascending to the throne, Abdullah took steps toward broader freedoms and invested some of the country's vast oil wealth in large-scale education and infrastructure projects.
However, resistance from conservative factions hindered some of his efforts, leaving many women in particular disappointed by a lack of progress toward greater independence.
Under Abdullah's leadership, the country slowly squashed al Qaeda, capturing or killing its leaders in the kingdom, forcing the remnants underground and sidelining radical preachers.
It also took a more prominent role in international affairs.
Last year, it became the lead Arab nation in a U.S.-led coalition to eradicate the ultra-radical ISIS group in Iraq and Syria.