HARARE, Zimbabwe — Emmerson Mnangagwa, the military-backed politician whose allies ended Robert Mugabe’s 37-year rule over Zimbabwe, will be sworn in as the new president on Friday, the speaker of the country’s Parliament announced on Wednesday.

A day after Mr. Mugabe resigned under mounting pressure, the governing party, ZANU-PF, quickly nominated Mr. Mnangagwa, 75, to complete Mr. Mugabe’s term as president until the next election, which must be held by August.

Mr. Mnangagwa returned to Zimbabwe’s capital, Harare, from South Africa on Wednesday — the first time he has been seen in public since Mr. Mugabe fired him as vice president on Nov. 6. That dismissal triggered a chain of events that led to the country’s first transfer of power since independence in 1980. Mr. Mnangagwa’s ascension to the presidency will cap a military-led campaign that his allies have tried to coat with a veneer of legality.

To cheering supporters at the ZANU-PF headquarters, Mr. Mnangagwa said that leaders of the governing party had “constitutionally processed the resolutions which persuaded this moment to come by.” He said that the military intervention had reflected the people’s will and led to the start of a “new democracy.”