But Hailemariam, 47, a relatively little-known politician overshadowed by his mentor Meles Zenawi, who died Monday, faces tough challenges both internally and across the volatile Horn of Africa region.
Obama, who telephoned Hailemariam late Thursday, urged him to “use his leadership to enhance the Ethiopian government’s support for development, democracy, human rights and regional security,” the White House said.
Hailemariam has also met with South Sudan’s foreign minister and his Kenyan counterpart, who were in Addis Ababa on Thursday to pay their respects to Meles, who died aged 57 after a long illness in a Brussels hospital.
Official mourning continues for Meles, with thousands streaming past his flag-draped coffin in the National Palace on the first day open to the public, many wailing and falling to the ground with grief.
A large group of religious leaders in flowing robes carrying tall crosses gathered and prayed near the casket, which was displayed at the top of a set of red-carpeted stairs.
“I’ve lost my brother, my family, my everything! Don’t go, why, why, why,” screamed one man standing before the coffin, which was also surrounded by bunches of flowers and candles.
But the political process continues behind closed doors. Government spokesman Bereket Simon has said Hailemariam is expected to be formally sworn in at an emergency parliament session at “any time”.
In a rare peaceful handover of power in Ethiopian history, former water engineer Hailemariam takes over as interim leader from Meles, who had ruled with an iron fist since toppling dictator Mengistu Haile Mariam in 1991.
A close ally of Meles as deputy prime minister and foreign minister since 2010, Hailemariam was elected deputy chair of the ruling coalition, the Ethiopian Peoples’ Revolutionary Democratic Front (EPRDF), after the party’s fourth win, a landslide victory in 2010.
In a country long dominated by its major ethnic groups — most recently the Tigray people, like Meles — Hailemariam notably comes from the minority Wolayta people, from the Southern Nations, Nationalities and Peoples Region.
He served as president for the region — the most populous of Ethiopia’s nine ethnic regions — for five years.
But within the EPRDF, some of the most influential figures hail from the northern Tigray region, members of Meles’s ex-rebel group turned political party, the Tigrayan People’s Liberation Front (TPLF).
Analysts have suggested that several others are still jostling for power behind closed doors in the often secretive ruling coalition, even if in the open they may not take part in the running for the top job.
“Many see (Hailemariam) as a figurehead, part of a gesture by Meles and the ethnic Tigrayans to give more prominence to other ethnic groups,” said Jason Mosley of Britain’s Chatham House think-tank.
He is also a Protestant, unlike the majority of Ethiopia’s Christians, who follow Orthodox traditions.
But others say Hailemariam’s position outside the Tigray power base could in fact be a strength.
“His ethnicity is considered an advantage, because it is a minority in a multi-ethnic region and, most importantly, not from the numerically dominant Oromo or Amhara,” the International Crisis Group said in a recent report.
Critics also point to his relatively young age, lack of experience and the fact he was not part of the rebel movement which toppled Mengistu, unlike many in the ruling elite.
Instead, Hailemariam, who studied civil engineering in Addis Ababa, was completing his master’s degree at Finland’s Tampere University when Mengistu fell.
Hailemariam, while a protege of Meles, is therefore seen as an outsider by some.
“He is a political novice, he has not been part of the old guard, he has not been in the bushes fighting with the rebels,” Berhanu Nega, an exiled opposition leader and former mayor of Addis Ababa, told the BBC.
“He is a Medvedev for a group of Putins in the ruling party with their own internal squabbles,” he added, drawing parallels with Russian political dynamics.
The government however has insisted Hailemariam will remain in the post until elections due in 2015, although he must first be formally chosen as head of the EPRDF, likely later this year.
“The secession issue has been settled for good,” said spokesman Bereket.
