HAVANA — The Cuban government on Wednesday selected First Vice President Miguel Mario Diaz-Canel Bermudez as the sole candidate to succeed President Raul Castro in a transition aimed at ensuring that the country’s single-party system outlasts the aging revolutionaries who created it.

The certain approval of Diaz-Canel, 57, by members of the National Assembly will install someone from outside the Castro family in the country’s highest government office for the first time in nearly six decades.

Castro, 86, will remain head of the Communist Party, designated by the constitution as “the superior guiding force of society and the state.”

As a result, Castro will remain the most powerful person in Cuba for the time being. His departure from the presidency is nonetheless a symbolically charged moment for a country accustomed to 60 years of absolute rule first by revolutionary leader Fidel Castro and, for the last decade, his younger brother.

Raul Castro is stepping down as president in an effort to guarantee that new leaders can maintain the government’s grip on power in the face of economic stagnation, an aging population and increasing disenchantment among younger generations.

“I like sticking with the ideas of President Fidel Castro because he did a lot for the people of Cuba, but we need rejuvenation, above all in the economy,” said Melissa Mederos, 21, a schoolteacher. “Diaz-Canel needs to work hard on the economy, because people need to live a little better.”

Most Cubans know their first vice president as an uncharismatic figure who until recently maintained a public profile so low it was virtually nonexistent.

That image changed slightly this year as state media placed an increasing spotlight on Diaz-Canel’s appearances, including remarks to the media last month that included his promise to make Cuba’s government more responsive to its people.

“We’re building a relationship between the government and the people here,” he said then after casting a ballot for members of the National Assembly. “The lives of those who will be elected have to be focused on relating to the people, listening to the people, investigating their problems and encouraging debate.”

Diaz-Canel gained prominence in central Villa Clara province as the top Communist Party official, a post equivalent to governor. There, people described him as a hard-working, modest-living technocrat dedicated to improving public services. He became higher education minister in 2009 before moving into the vice presidency.

International observers and Cubans alike will be scrutinizing every move he makes after he officially takes office Thursday — on the anniversary of the defeat of U.S.-backed invaders at the Bay of Pigs in 1961.

Meanwhile, U.S. Sen. Marco Rubio, R-Fla., said the selection of Castro’s successor is a “charade” that will not bring change to the island.

Rubio said that with Diaz-Canel, “the regime will remain an enemy of democracy, human rights and the impartial rule of law.”

Two years after taking over from his ailing brother in 2006, Raul Castro launched a series of reforms that expanded Cuba’s private sector to nearly 600,000 people and allowed citizens greater freedom to travel and access to information.

He has failed to fix the generally unproductive and highly subsidized state-run businesses that, along with a Soviet-model bureaucracy, employ three of every four Cubans. State salaries average $30 a month, leaving workers struggling to feed their families, and often dependent on corruption or remittances from relatives overseas.

Castro’s moves to open the economy have largely been frozen or reversed.

“I don’t want to see a capitalist system, hopefully that doesn’t come here, but we have to fix the economy,” said Roberto Sanchez, 41, a construction worker. “I’d like to have more opportunity, to buy a car, and have a few possessions.”

As in Cuba’s legislative elections, all of the leaders selected Wednesday were selected by a government-appointed commission.

The Candidacy Commission also nominated another six vice presidents of the Council of State, Cuba’s highest government body. Only one, Ramiro Valdez, 85, was among the revolutionaries who fought with the Castros in the late 1950s in the eastern Sierra Maestra mountains.

State media went into overdrive Wednesday with a single message: Cuba’s system is continuing in the face of change.

Fidel Castro was prime minister and president from 1959 until he fell ill in 2006.