The sidelined AIADMK leader TTV Dhinakaran, who won the RK Nagar by-election, will formally take charge as the MLA in Tamil Nadu Secretariat on Friday.
Dhinakaran will take oath as MLA at the Speaker's chamber at around 1.30 pm.
He had on Sunday won the RK Nagar by-polls by a margin of 40,707 votes.
The key candidates in the fray besides Dhinakaran were AIADMK's E Madhusudhanan, DMK candidate N Maruthu Ganesh and BJP's Karu Nagarajan.
Dhinakaran got 89,013 votes, while Madhusudhanan secured 48,306 votes. Ganesh got 24,651 votes, while Nagarajan amassed 1417 votes.
The RK Nagar constituency went to polls on December 21, necessitated by the death of former Tamil Nadu chief minister J Jayalalithaa in December last year.
The election was earlier scheduled on April 12, but was cancelled following an alleged vote-for-cash scam.