LJUBLJANA, Slovenia — No candidate won an outright majority in Slovenia’s presidential election and a runoff will be held next month ­between the incumbent and a former prime minister, an ­exit poll predicted on Sunday.

Borut Pahor, former prime minister, will finish first with 41.9 percent of the vote, followed by President Danilo Turk, with 37.2 percent, and center-right candidate Milan Zver at 20.9 percent, said the poll, conducted by the Mediana agency and broadcast on state television.