The Ethiopian authorities said he had died in a hospital “abroad” — a European Commission spokesmantold reporters that it was in Brussels — just before midnight after getting a secondary infection. His failing health had been shrouded in mystery for months.

A former rebel leader who had dropped out of medical school in the 1970s to fight Ethiopia’s former Communist government, Mr. Meles was considered one of Africa’s shrewdest and most intelligent leaders. He was known to be a voracious reader with a steel-trap mind who could rapidly digest mountains of statistics and quote large chunks of Shakespeare. He worked closely with Washington to combat Muslim extremism in the Horn of Africa, though there were growing complaints, even among his backers, about his penchant for violently quashing any dissent.

In the 1990s, Mr. Meles was widely hailed as a pivotal member of the “new generation” of African leaders who had overthrown dictators and would usher in democracy. But while he has often been praised for his development efforts, Mr. Meles steadily concentrated power after becoming prime minister in 1995, boxing out rivals and creating a fearful atmosphere where criticism was not tolerated and journalists and opposition politicians were jailed.

Hailemariam Desalegn, the minister of foreign affairs and deputy prime minister, will become the new premier, the government announced on Tuesday. It was considered unlikely that he would command the same authority as Mr. Meles, and some were sure to see him as little more than a figurehead for a government that remains tightly controlled by Mr. Meles’s Tigrayan ethnic minority group from northern Ethiopia.

Many analysts said they did not expect drastic policy shifts anytime soon and predicted that Ethiopia would remain a close American ally.

Mr. Meles vanished from public view in June, and Western officials had said he was suffering from liver cancer.

In mid-July, the government’s chief spokesman, Bereket Simon, scoffed at the notion that Mr. Meles was seriously ill, saying that “His health condition is very good and stable” and that he was just “taking some rest.”

Ethiopia is widely considered one of Africa’s most repressive governments, though it continues to get around $1 billion of American aid each year. It is also a close American military ally, and American officials have said that one of the Central Intelligence Agency’s favorite partners to fight Muslim extremism in Africa is the Ethiopian military and security services.

Last year, the Ethiopian government sentenced two Swedish journalists to 11 years in prison after they were caught inside Ethiopia traveling with a rebel group. This year, it jailed a prominent Ethiopian journalist on vague terrorism charges.

In the past few months, the Ethiopian government has been accused of killing and displacing members of traditional groups who live in the Omo River valley in southern Ethiopia so the government can build a large hydroelectric dam and lease land to foreign sugar companies.

Mr. Meles was seen as the mastermind behind many of his government’s plans. While many human rights groups vilified him, some development experts celebrated him, saying Ethiopia has vastly better famine prevention programs than it did when Mr. Meles’s insurgent group seized power in 1991.

Under Mr. Meles, especially in recent years, Ethiopia has invested heavily in public infrastructure and branched into competitive businesses like flower farming.

Ethiopia has been considered one of the fastest-growing, non-oil-dependent economies in the developing world, with the economy expanding above 7 percent last year. Though it remains poor, with a per capita of income of more than $1,000, some credited Mr. Meles with making strides toward the United Nations Millennium Development Goals. Others have complained that aid and other social benefits are awarded only to allies of the governing party.

Mr. Meles played an outsized role in the region, recently helping try to broker peace between Sudan and the newly independent nation of South Sudan.