The election was necessitated due to the death of her husband in November last year.
BJP candidate Tsering Lhamu was on Friday declared elected the MLA of Lumla constituency in Arunachal Pradesh's Tawang district without a contest.
Tsering Lhamu, the wife of former MLA Jambey Tashi, was the only candidate who filed her nomination for the by-election to the seat. The by-election was necessitated due to the death of her husband in November last year.
Returning Officer Rinchin Dorjee Thungon declared the result at 3 pm after the deadline for the withdrawal of candidature was over, Chief Electoral Officer (CEO) Liken Koyu said.
Ms Lhamu was handed the election certificate, he said.
Though People's Party of Arunachal (PPA) named former 'gaon burha' or village headman Leki Norbu as its candidate for the by-election, he withdrew from the race.
Mr Tashi, who represented the constituency for three consecutive terms since 2009, died at a hospital in Guwahati at the age of 48.
Assembly elections in the northeastern state will be due next year, and are likely to be held simultaneously with the Lok Sabha polls.
With this win, the ruling BJP's tally in the 60-member House remained at 49.
The opposition Congress and National Peoples' Party (NPP) have four MLAs each, while there are three Independent MLAs.
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