DMK is the single largest opposition party in the 234-member House with its 89 MLAs including party Chief M Karunanidhi and Stalin.
In the previous assembly, DMK could manage only 23 MLAs, while DMDK (Desiya Murpokku Dravida Kazhagam), which won 29 seats as AIADMK (All India Anna Dravida Munnetra Kazhagam) ally, was the main opposition party and its founder, Vijayakant, the opposition leader.
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Stalin was elected as leader at a meeting of DMK MLAs which was also attended by Karunanidhi, who represents his native Thiruvarur constituency.
Often tipped as Karunanidhi's political heir apparent, Stalin has in the past held the post of Chennai Mayor between 1996-2002 and started off as a minister in the Karunanidhi cabinet in 2006 when he was allotted Rural Development and Local Administration.
He was later elevated as Deputy Chief Minister and has been holding party posts of Chief of Youth Wing and DMK Treasurer.
He was first elected to the state assembly in 1989 and this is his sixth term as legislator. He was party's floor leader in the previous assembly also.
Stalin was elected from Kolathur in the May 2016 polls for a successive term.
On Tuesday, senior leader Durai Murugan was elected Deputy Leader of DMK Legislature wing while R Sakkarapani is the party's whip in the assembly.