Mr. Mekonnen said Mr. Abiy would face many challenges in unifying and leading the country.
“It will be a struggle to change the status quo,” he said. “He is energetic and reformist, but that could also shake the government.”
A movement for change began in 2015 with street protests in the Oromia region, which includes Addis Ababa, and spread to other regions unhappy with the dominant party’s grip on economic and political power. At least 700 people have died in the protests.
Earlier this year, Ethiopia’s governing coalition had made concessions to popular demands for change, releasing hundreds of political prisoners, a move championed by Oromo activists.
The resignation in February of Prime Minister Hailemariam Desalegn, was widely viewed as an acknowledgment that those concessions had not gone far enough — making it virtually inevitable, experts said, that the next prime minister would come from the Oromo group.
Although the country is led by a coalition of four parties, the minority Tigrayan party has long been seen as controlling the political and economic life of Ethiopia.
Mr. Abiy, 41, was named the leader of the Oromo People’s Democratic Organization, one of the four parties in the coalition just last month. Young and charismatic, he delivers public statements in multiple languages, including English, to appeal to people beyond his own ethnic group.
“Abiy was probably the most popular candidate, the most favored candidate, by the public, broadly speaking,” said Hallelujah Lulie, a political analyst in Addis Ababa.
That support has come in part because of the welcoming way in which Mr. Abiy has spoken about the street protests and demands for change, Mr. Hallelujah said — but he has always done so as a political insider, equally attuned to the demands of power inside the governing coalition.
Previously, Mr. Abiy has been a soldier, an intelligence officer and a minister of science and technology, as well as the vice president of the Oromia region.
The news was greeted with unexpected calm across Ethiopia, and with hope that life — and business — will go back to normal. Leaders of large companies have complained that foreign exchange has been difficult to come by, making business and investment difficult.
“Our businesses were crumbling,” said Daniel Gebre, who runs an electronics maintenance shop in Addis Ababa. “It was very difficult to do anything because the roads were blocked and there was a shortage of goods.”
Mr. Abiy’s appointment as prime minister will become official with the approval of Parliament, expected in the next two weeks.
Mr. Mekonnen said the first real signs of the new prime minister’s strength and intentions would come when he named his cabinet — and if he decided to lift the state of emergency.
His handling of the security agencies will be equally important. The intelligence and security services control the military, but they also have a hand in the economy, Mr. Hallelujah, the analyst, said.
Many Ethiopians perceive the security services — and the money and power they control — as dominated by members of the Tigrayan ethnic group, a wealthy minority that also controlled the governing coalition, until the Oromia protests forced talk of political change.
But some people warn that the success of the street protests from Mr. Abiy’s region may also be his downfall, because sometimes violent protests can result in changes in power.