He stepped off a gray jumbo jet to the excited but subdued applause of a few airport employees in neon vests. At least one fellow passenger giddily approached him for a selfie.

Nearly three months after fleeing Mozambique, saying he feared for his life, opposition leader Venâncio Mondlane made a grand return on Thursday to try to claim what he insists is rightfully his: the presidency.

Mozambique is scheduled to inaugurate a new president from the long-governing Frelimo party on Wednesday. Daniel Chapo of Frelimo won with 65 percent of the vote in the October election, according to the nation’s highest court. By the official tally, Mr. Mondlane got just 24 percent.

After several independent election observers identified irregularities in the vote, Mr. Mondlane spent months arguing the race was stolen, calling on his supporters to take to the streets. Some protests have descended into violence, with at least 250 people killed during a police response that human rights groups have called unnecessarily brutal.

Mr. Mondlane’s return comes at a delicate moment for this mineral- and gas-rich nation of 33 million. The government is struggling to address housing and debt crises, and to quell a yearslong insurgency backed by the Islamic State. Regional leaders like South Africa have sent envoys to try to broker a resolution to a political deadlock that has stymied trade and threatens further economic damage.