"Jharna Das Baidya got 49 votes while Congress candidate Nath secured only 10 votes," assembly secretary Bamdeb Majumder, who was also the returning officer for the election, told reporters.
Ailing Communist Party of India-Marxist legislator and minister (without portfolio) Bhanu Lal Saha could not vote as he was out of Tripura for cancer treatment.
The CPI-M candidate's win was almost certain as the strength of the ruling Left Front in the 60-member house is 50, with the CPI-M alone having 48 members. The main opposition Congress has 10 members.
Before being elected to the upper house of parliament, Baidya had served as the chairperson of the State Social Welfare Board.
The 53-year-old belongs to the Scheduled Caste community and is a senior member of the All India Democratic Women's Association, a women's body of the CPI-M.