The ruling Congress won the Dantewada assembly by-poll in Chhattisgarh on Friday.
The Bharatiya Janata Party, which lost the seat, accused the Congress of misusing government machinery to win the election.
Congress's Devti Karma won the bypoll for the seat, reserved for Scheduled Tribes, by a margin of 11,192 votes, a poll official said.
Devti Karma is the wife of senior Congress leader Mahendra Karma who was killed in the Jhiram Valley Naxal attack in 2013.
Karma polled 50,028 votes while her nearest rival, the BJP's Ojaswi Mandavi, secured 38,836 votes, he said.
Communist Party of India candidate Bhimsen Mandavi stood third with 7,664 votes, he said.
Voting was held on September 23. The voting percentage was 60.59 per cent.
The byelection was necessitated by the death of BJP MLA Bhima Mandavi in a Maoist attack in April. The BJP had fielded his wife Ojaswi in the by-election.
Dantewada was the only seat in the Bastar division that the BJP had managed to win in last year's assembly polls.
In the 2018 assembly elections, Devti Karma had lost to Bhima Mandavi by a narrow margin of 2,172 votes.
Reacting to the result, BJP leader and former chief minister Raman Singh alleged that the district collector acted like the "Congress' chief election campaigner".
"I have seen several elections, but for the first time I saw an unusual thing. The district collector seemed to be acting like the chief election campaigner of the Congress and entire administration was working with him," Singh said.
Neither he nor other BJP leaders were allowed to visit several areas of the constituency for campaigning, while the Congressmen faced no such difficulty, he alleged.
Singh, however, congratulated Devti Karma, and said Ojaswi Mandavi put up a tough fight under "adverse conditions".
The Congress said the victory was a result of the state government's pro-farmer and pro-tribal policies.
"By giving their blessings in the Dantewada bypoll, people have reposed faith in the work being done by the state government to create a new Chhattisgarh. This is the victory of dreams of Late Mahendra Karma. Congratulations and wishes to Devti Karma," Chief Minister Bhupesh Baghel tweeted.
The state BJP, meanwhile, held a meeting on Friday to gear up for the Chitrakot assembly bypoll scheduled for October 21, necessitated after Congress MLA Deepak Baij was elected to the Lok Sabha from Bastar.
In the 2018 assembly polls, the Congress had won 68 seats in the 90-member house, with the BJP winning only 15.
But in the Lok Sabha elections, the BJP won nine of the 11 Lok Sabha seats.