Tripura assembly Speaker Ratan Chakraborty administered the oath of office and secrecy to Saha, who on Monday resigned from the Rajya Sabha.
Later, the Chief Minister tweeted: “Took oath as a Member of Tripura Legislative Assembly, today. With the help of colleagues in the house and under the leadership of PM Narendra Modi, we will definitely take forward the development works of the state.”
Contesting the elections for the first time in his three-decade long political career, the 69-year-old Congress-turned-BJP leader won from the Town Bordowali Assembly constituency.
Saha, who is also the state unit chief of the BJP, took oath as the Chief Minister on May 15, a day after Biplab Kumar Deb resigned from the top post.
To fulfil the constitutional obligation, he had to become a member of the Assembly within six months.
In the June 23 by-polls, results of which was declared on June 26, the ruling Bharatiya Janata Party won three of the four seats including that of Manik Saha who defeated Congress candidate Asish Kumar Saha by a margin of 6,104 votes.
The other three newly elected members — Sudip Roy Barman (Congress) and Malina Debnath and Swapna Das (Paul), both BJP — took oath as members of the Tripura assembly on June 28.