DUBLIN — Sinn Fein, a leftist party long ostracized from Irish politics over its ties to sectarian violence, won the popular vote and seized its largest-ever share of parliamentary seats in the country’s national elections this weekend, according to results released on Sunday.

The vote loosened a 90-year stranglehold on power by two center-right parties in Ireland and put Sinn Fein on the doorstep of joining a coalition government, a remarkable rebuke to a political establishment that tried to paint it as aberrant and unelectable throughout the campaign.

Defying a reputation for extreme risk aversion, Irish voters ignored those warnings.

They gave Sinn Fein more votes than Ireland’s prime minister, Leo Varadkar, in his Dublin district, though Ireland’s system of vote allocation allowed Mr. Varadkar to hold onto his parliamentary seat.

Irish voters delivered more votes to left-wing parties than they had in decades, realigning a center-heavy political system along class and ideological lines.