Former student protest leader Gabriel Boric has defeated conservative Jose Antonio Kast in Chile’s presidential election, becoming the nation’s youngest leader in modern times.

Kast conceded defeat on Sunday with Boric holding a sizable lead – at around 55% to 45% — with more than two-thirds of the votes counted. Boric, 35, has pledged to expand Chile’s social programs, nationalize the pension system and raise government revenue through taxes on the massive mining companies that operate in the country.

Acabo de hablar con @gabrielboric y lo he felicitado por su gran triunfo. Desde hoy es el Presidente electo de Chile y merece todo nuestro respeto y colaboración constructiva. Chile siempre está primero ??✌️

Although the race marked one of the most contentious and polarizing presidential elections since Chile returned to democracy three decades ago, Kast congratulated his rival only about 90 minutes after polls closed. “From today, he is the elected president of Chile and deserves all our respect and constructive collaboration,” Kast said.

Sunday’s runoff election was necessary because none of the seven  candidates received more than 30% of the votes cast in last month’s first round. Kast, a Catholic who campaigned on tax cuts and a pledge to halt immigration, came close to securing victory in November, winning nearly 28% of votes. Boric, who took 26% in the first round, was boosted by strong urban support in Santiago.

Boric became the first Chilean president to win a runoff after failing to lead the field in the first round. He may have been helped by revelations this month that Kast’s father was a German Nazi during World War II, but Boric also alienated some Jewish voters by demanding that Chile’s Jews denounce Israel’s occupation of the West Bank.

The new president will take the helm at a pivotal time, as Chile is drafting a new constitution to replace the one adopted under former dictator General Augusto Pinochet in 1973. Boric has promised to protect abortion rights and same-sex marriage and to expand the rights of indigenous Chileans, including the Mapuche indians.

Boric will take office in March, succeeding Sebastian Piñera, a businessman-turned-politician who became the first Chilean conservative to win a presidential election since military rule ended in 1990.