ISTANBUL — The main Syrian opposition coalition on Saturday elected Ahmad Tomeh, a dentist and longtime dissident, to be the opposition’s provisional prime minister, in the group’s latest effort to improve its standing inside the country and attract greater support from foreign nations.

Mr. Tomeh, 48, who ran unopposed, was said to be a consensus candidate accepted by a secular-leaning coalition within the group and the Syrian Muslim Brotherhood. He replaces Ghassan Hitto, a Syrian-American businessman who failed to name a cabinet and resigned in July, reportedly after one of the coalition’s principal supporters, Saudi Arabia, signaled its displeasure with him.

With its shifting constellation of leaders, the opposition coalition, known as the Syrian National Council, has cemented a reputation for infighting, and many Syrians disparage it as an exile movement beholden to the agendas of its foreign supporters. While the group has gained international recognition, its leaders complain that it receives insufficient support.

Mr. Tomeh, who comes from the eastern province of Deir al-Zour, spent time in jail as a political prisoner and was one of the signers of the Damascus Declaration in 2005, a statement that demanded changes from the government of President Bashar al-Assad.