NEW DELHI—Indian Prime Minister Narendra Modi’s party made significant gains in elections in the state of Karnataka, giving it a boost ahead of national elections early next year.
Near the end of the vote count Tuesday night, the Bharatiya Janata Party had won 103 seats and was leading in one more. That boosted its tally by more than 60 seats, compared with the 40 it won in 2013 when the state’s elections were last held, according to the Election Commission of India. To form a majority government in Karnataka, 113 seats are...