Odumegwu Ojukwu, who attracted international attention when he led the Republic of Biafra’s secession from Nigeria in 1967 and subsequently waged a civil war that left more than 1 million dead — many of them children who succumbed to starvation — has died in London. He was 78.

News accounts reported that he died Nov. 25 or 26. A cause of death could not be confirmed.

Mr. Ojukwu was an unlikely rebel leader. The son of a Ni­ger­ian millionaire knighted by the Queen of England, he grew up in a mansion and attended a private high school in Surrey, England, where he set a school record for the discus throw.

At Lincoln College at the University of Oxford, he played on the rugby team and was known for his flashy clothes and red sports car. He graduated in 1955, then returned to Nigeria. He rebuffed his father’s offer to join the family transport business and enrolled in civil service, working on community projects building roads and digging culverts.

He later joined the military — partly to spite his father, he said, but also because he sensed that “Nigeria was headed for an upheaval and that the army was the place to be when the time came.”

Odumegwu Ojukwu, the Biafran head of state, addressing a joint session of the consultative assembly and house at Owerri, on Jan. 31, 1968. (Anthony Astrachan/The Washington Post)

The most populous nation in Africa, Nigeria is on the western coast, just north of the equator. For decades, Nigeria was a British colony until declaring independence in 1960. Three years later, Nigeria became a republic within the British commonwealth.

Mr. Ojukwu rose through the army ranks before the chaos he predicted arrived in January 1966. A gang of officers overthrew the government in a coup and assassinated the prime minister.

Although Mr. Ojukwu didn’t participate in the coup, he was made the military governor of Nigeria’s oil-rich eastern region, home to many ethnic Ibo Christians like himself.

A counter-coup followed a few months later that left Nigeria in disarray. Throughout the power struggle, Mr. Ojukwu kept the eastern region running smoothly and mostly independent of federal rule.

In September 1966, 20,000 Ibo were massacred in pogroms in the Muslim-dominated northern region. Mr. Ojukwu called the unprovoked aggression “organized, wanton fratricide.”

Mr. Ojukwu grew a thick, bushy beard “as a sign of mourning,” he said, for the injustice caused to the Ibo. He acceded to mounting demands of an Ibo-led secession of the eastern region, a total area of 30,000 square miles.

He announced the birth of the Republic of Biafra during a radio address at 3 a.m. on May 30, 1967. The ceremony featured a 42-gun salute and champagne served from waiters in white coats. He named his country after a Ni­ger­ian coastal inlet and chose Jean Sibelius’s “Finlandia” as the melody for his nation’s anthem.

For much of his 30-month rule, he was a revered figure among his people. A raconteur who charmed journalists, he quoted from Shakespeare and spoke authoritatively about the reign of King Louis XIV of France. He landed on the cover of Time magazine in 1968 and gained sympathetic followers such as the celebrated Nigerian author Chinua Achebe, who moved to Biafra’s capital and later wrote many books inspired by the secession.

“A state that failed to safeguard the lives of its citizens has no claim to their allegiance,” Achebe told a reporter. “Biafrans will not live in Nigeria and if they are constrained to do so by force, this part of the world will not know peace.”

Soon after Biafra declared independence, Nigeria struck back violently. From the outset, Biafra’s odds for survival were minimal. The Ni­ger­ian army outnumbered the Biafrans as many as 4 to 1. While the Biafrans carried single-shot rifles and five rounds of ammunition, the Nigerians were supplied heavy weapons from Britain and fighter jets from Egypt.

Facing such a remote victory, Mr. Ojukwu told his army to “be prepared to die so that our children may live.”

As months of combat progressed, Biafra was surrounded by Ni­ger­ian forces, cutting off food supplies. As a result, there was widespread starvation in Biafra. Mr. Ojukwu contacted a Swiss public relations firm, which sent out images to world publications showing Biafran children with swollen bellies and ribs as thin as rifle barrels.

Newspapers referred to the Biafran famine as a modern Holocaust, a comparison Mr. Ojukwu welcomed. He had read Leon Uris’s novel “Exodus” about the foundation of Israel.

“The Israelis are hardworking, enterprising people. So are we,” Mr. Ojukwu once said. “They’ve suffered from pogroms. So have we. In many ways, we share the same promise, and the same problems.”

Georgetown University visiting associate professor Herbert Howe said in an interview that the famine in Biafra was one of the first modern humanitarian crises to serve as an international cause celebre.

Time magazine reported that up to 1,000 people a day died of starvation in Biafra. To combat a protein-deficiency disease, Mr. Ojukwu’s government told Biafrans to eat rats, dogs and lizards.

The Biafran crisis “united Ted Kennedy and Strom Thurmond to push for changes in U.S. policy,” Howe said, referring to the liberal and right-wing senators, respectively. Governments around the world, including the United States (which was officially neutral), shipped food to Biafra by the planeload.

More than 1 million Biafrans were estimated to have died because of starvation. With the Ni­ger­ian army closing in, Biafra’s borders shrank, and Mr. Ojukwu became isolated.

In January 1970, he left in voluntary exile with his family and some close aides on an airliner packed with three tons of luggage and his white Mercedes-Benz. Biafra soon disintegrated. Only five countries — Gabon, Tanzania, Ivory Coast, Zambia and Haiti — officially recognized Biafra during its existence.

“Although he was very urbane and ambitious, he may have been deeply flawed and a political opportunist who played the ethnic card for all it was worth,” Howe said, noting that Mr. Ojukwu’s 30-month reign “amounted to incredible unity, incredible suffering and incredible courage, regardless of the rights and wrongs that occurred.”

Chukwuemeka Odumegwu Ojukwu was born Nov. 4, 1933, in Zungeru, Nigeria. He was married three times. A complete list of his survivors could not be determined.

In exile, Mr. Ojukwu lived for many years in the Ivory Coast before returning to Nigeria in the 1980s. Pardoned by the government, he attempted a second run at politics and was defeated in his presidential bids.