For years, Ahmed al-Shara was the leader of a rebel group once allied with Al Qaeda that was fighting the rule of President Bashar al-Assad in Syria.

After a rebel coalition led by his group, Hayat Tahrir al-Sham, toppled Mr. al-Assad in December, Mr. al-Shara suddenly found himself president.

He faces a dizzying array of challenges as his country — which the Assad family ruled for five decades — undergoes a momentous period of transition.

He must rebuild a country destroyed by war and bankrupted by sanctions. He has to persuade the West he is a reliable partner despite his previous affiliations with Al Qaeda and navigate geopolitical tensions playing out on his territory between Turkey to the north and Israel to the south. And he needs to forge a new relationship with Russia, which was allied with Mr. al-Assad.

All of this involves navigating a far more complex geopolitical situation than he had as a rebel leader governing a tiny slice of Syrian territory. It also comes at a precarious moment of upheaval in the Middle East.

Mr. al-Shara sat down for an interview this month at the presidential palace in the capital, Damascus, to discuss the challenges his new government faces and his vision for Syria.