An agreement was signed between the top leadership of the two parties here in the presence of Tamil Nadu Chief Minister K Palaniswami and his deputy O Panneerselvam and Vijayakanth and DMDK Treasurer and his wife Premalatha.
Talking to reporters, Panneerselvam, the coordinator of the rulling party, said it was a committed alliance.
Premalatha pledged her party's support to the AIADMK in the bypolls to 18 assembly seats and local body elections, expected in May.
AIADMK has already finalised seat sharing with BJP and PMK and a few smaller outfits for the Lok Sabha elections.
It has alloted seven seats to PMK, five to the BJP in the state and the lone Puducherry seat to AINRC.
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