Venezuela’s embattled opposition announced on Friday that it was naming a new candidate to face off against President Nicolas Maduro this summer, giving renewed hope to the country’s push toward democracy.

The country’s highest court in January barred the previous candidate, the former lawmaker María Corina Machado, from running, leading many Venezuelans to question how free and fair the election would be. The decision raised questions over whether Ms. Machado’s party, Come Venezuela, would try to insist on her candidacy or coalesce around another candidate.

On Friday. leaders of several opposition parties announced that Corina Yoris, a philosophy professor, would run instead in the elections on July 28, a move that analysts saw as a surprising show of unity.

“This is huge,” said Laura Dib, who directs the Venezuela program at the Washington Office on Latin America, a human rights organization. “It is truly amazing to see the opposition united around a single strategy and showing that they are not backing off.”

In October, Mr. Maduro signed an accord with the country’s opposition and agreed to work toward a free and fair presidential vote. In the agreement, Mr. Maduro said he would hold an election before the end of this year, and, in exchange, the United States lifted some economic sanctions as a sign of good will.

But days later, Ms. Machado won more than 90 percent of the vote to choose an opposition candidate, in a primary election run by a commission without the involvement of the government. The decisive results emphasized her popularity and raised the prospect that she could beat Mr. Maduro in a general election.

Three months later, the country’s top court, filled with government loyalists, declared Ms. Machado ineligible to run over what the judges claimed were financial irregularities that occurred when she was a national legislator. The government also arrested several members of her campaign. Men on motorbikes have attacked supporters at her events.

Ms. Machado made Friday’s announcement in a news conference alongside Ms. Yoris just days before the March 25 deadline to register.

“We have found a person of my total trust, honorable, who is going to fulfill this procedure,” Ms. Machado said. “This was a decision that arose from within the discussion of the unitary forces and that gives us all confidence.”

Ms. Yoris was a member of the commission that helped organize October’s primary, raising speculation that the government might not allow her to register as a candidate. The government has questioned the opposition primary’s legitimacy and has taken legal aim at its organizers.

The fact that the head of another rival opposition party, Omar Barboza, opened the conference was a further show of unity, Ms. Dib said.

“We are heading toward a transition path in Venezuela,” Ms. Yoris said. “We are all necessary at this moment.”

Julie Turkewitz contributed reporting from Santander, Colombia.