The rebel coalition that seized control of Syria last month appointed its leader, Ahmed al-Shara, as president of the country to preside over a transitional period, Syrian state media reported on Wednesday.

A spokesman for the coalition, Col. Hassan Abdel Ghani, also declared that the Constitution had been nullified and the legislature and army formed under the country’s deposed dictator, Bashar al-Assad, were dissolved, according to Syria’s state news agency, SANA.

The declarations amounted to the country’s first official steps toward establishing a new government after the rebel coalition, Hayat Tahrir al-Sham, swept into the capital, Damascus, last month in a lightning offensive that toppled Mr. al-Assad. Mr. al-Shara, who led that coalition, has since been serving as the country’s de facto leader.

As the president of the transitional government, Mr. al-Shara will be at the helm of a once unimaginable period of transition in Syria, which had been ruled by the iron fist of the Assad family for more than 50 years.