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If Gustavo Petro becomes president of Colombia in an election later this month or in a June runoff, as opinion polls suggest, observers may note a trend in Latin America: In recent years voters from Mexico to Chile have tossed out entrenched right-wing governments. Yet that would not mean the region is turning left. Most Latinos describe themselves as centrist. They seek change to reduce economic disparities and create more inclusive societies.

For sure, Mr. Petro would be Colombia’s first leftist president. His running mate, Francia Márquez, would be the first woman and person of African heritage elected vice president. But his rise would be relevant far beyond his politics or within the region’s geographic boundaries. His biography holds a lesson for societies on how to disarm insurgencies and terrorist movements through reconciliation and political accommodation.

In his youth Mr. Petro was active in Colombia’s 19th of April Movement, or M-19, a faction that sought democratic change through guerrilla tactics in the 1970s and 1980s. The group morphed into a political party following a 1990 peace accord with the government. Several of its members went on to impactful political careers. Mr. Petro, a trained economist, served two terms as mayor of the capital, Bogotá.

Colombia replicated its model in a 2016 agreement that ended a 52-year war with another guerrilla faction known by its Spanish acronym, FARC. The deal guaranteed political inclusion for disarmament.

In one form or another, similar peacemaking dialogues are underway in communities along Pakistan’s border with Afghanistan and in countries battling Islamist groups in Africa’s Sahel region. “The best thing we can do for peace is to reintegrate those who, in the moment of despair, became terrorists but now want to become citizens and to contribute to the well-being of their brothers and sisters,” said United Nations Secretary-General António Guterres during a visit last week to camps for demobilizing jihadis in Maiduguri, Nigeria.

Persuading guerrillas to seek change by ballots rather than by bullets takes patience. As several African countries have discovered, former anti-colonial liberation movements often struggled when they moved from bush camps to the halls of power. But there is a growing consensus, among academics if not diplomats, that the international community’s standard post-conflict formula of organizing elections and promoting civil society has been ineffective.

Uruguay illustrates the ultimate dividend of bringing former rebels and their support networks into democracy. In the mid-1980s, a newly elected government offered amnesty to imprisoned members of a leftist group called the Tupamaros following the collapse of an authoritarian regime. The group formed a new political coalition and, within 20 years, won the presidency. Similar successful transitions have happened in Brazil and Bolivia.

“The ex-guerrillas tend to be the most consistently pragmatic and pro-democratic forces on the left,” Oxford Professor Timothy Power noted in the Miami Herald at the time. “Those who have been arrested, exiled, or tortured tend to value democracy and civil liberties more than other leftists who have not yet stuck their hand into the fire of repression.”

If Mr. Petro brings similar sentiments to Colombia’s presidency, it would represent quite a path from guerrilla to democratic politician. It is a path that offers hope to other societies working their way out of violent conflict.