Gustavo Petro, a former guerrilla who wants to transform Colombia’s business-friendly economic model, has been elected to the presidency, potentially setting up the most radical change of course in the Andean nation’s recent history.

Petro, a former mayor of Bogota, took 50.5% to 47.3% for construction magnate Rodolfo Hernandez in Sunday’s runoff with almost all votes counted, according to Colombia’s electoral authorities. Hernandez conceded in a video message.

Petro, 62, will now take office on Aug. 7. His running mate, Francia Marquez, a 40-year-old environmental activist, will become the country’s first Afro-Colombian vice president.