Why Colombian voters picked their first leftist president

Colombia will be governed by a leftist president for the first time after former rebel Gustavo Petro narrowly defeated a real estate millionaire in a runoff election that underscored people’s disgust with the country’s traditional politicians.

Petro’s third attempt to win the presidency earned him 50.48% of the votes Sunday, while political outsider Rodolfo Hernández got 47.26%, according to results released by election authorities.

The election came as Colombians struggle with rising inequality, inflation and violence — factors that led voters in the election’s first round last month to punish...