Edapaddi Palaniswami, who was nominated for the post by late chief minister Jayalalitha's aide Sasikala Natarajan, will be sworn in as TN CM.
Sasikala, who only uses one name, was nominated as chief minister by the state's ruling party.
However her conviction in a corruption case means she cannot hold office.
She had to surrender to authorities to serve a four-year jail term on 15th Feb 2017, but appointed Mr Palaniswami before she left.
He met State Governor C Vidyasagar Rao on 16th Feb 2017 morning, with proof that he had the support of a majority of lawmakers.
Mr Rao agreed to appoint him as chief minister on condition that he proves his majority in the state assembly within 15 days.
O Panneerselvam, who was sworn in as caretaker chief minister after the death of Jayalalitha in December, was vacillating between rebellion and loyalty to Sasikala.
Sasikala's elevation by the party had been questioned by acting chief minister O Panneerselvam, who said he had been "forced" to resign to make way for her.
Her candidacy for the top job had been questioned, since she has never been elected to public office.
Sasikala's role was always that of aide and confidante.VK Sasikala/Sasikala Natarajan
- Vivekanandan Krishnaveni Sasikala, is also known as Sasikala Natarajan
- She is an Indian politician who is the acting general secretary of All India Anna Dravida Munnetra Kazhagam.
- Born: 1957, Mannargudi
- Party: All India Anna Dravida Munnetra Kazhagam