ASUNCION, Paraguay — A former Roman Catholic bishop, Fernando Lugo, won a historic victory in Paraguay’s presidential election yesterday, ending more than six decades of one-party rule with a mandate to help the nation’s poor and indigenous.

His rival, Blanca Ovelar, conceded defeat after a closely fought race to lead this poor, agrarian nation where Mr. Ovelar’s Colorado Party is the only ruling party most people have ever known.

News of the win by Mr. Lugo, dubbed the “bishop of the poor,” set off massive parties in cities across Paraguay with horn-honking caravans of cars blaring music. Others stamped on torn-down banners of the Colorado Party, which many Paraguayans blame for decades of corruption by political elites.

The triumph by Mr. Lugo’s eclectic opposition alliance also marked the latest in a series of election wins by leftist, or center-left, leaders in South America.

“I invite Paraguayans of all political types, even the ones who don’t share our ideals, to help this country that was once great be great again,” Mr. Lugo told cheering supporters.

“This is the Paraguay that I dream of — of many colors, many faces,” he said in reference to his pluralistic coalition, Patriotic Alliance for Change.

A journalism student, Andrea Ramirez, 19, waved a Paraguayan flag at the rally. “I voted for the first time and am very happy. The shameless and cynical ones have lost.”

With 12,983 of some 14,000 balloting stations counted, officials said Mr. Lugo had 41% of the vote, Mr. Ovelar had 31%, and former army chief Lino Oviedo had 22%. Election officials said that tally accounts for nearly 1.5 million votes — out of a 2.8 million electorate.

Officials said 66% of the electorate cast ballots, a record number in a presidential election since the 1989 restoration of democracy.