Puthiya Thamizhagam (PT), which is part of the DMK alliance, will be contesting four seats in the upcoming assembly elections in Tamil Nadu.
The pact was signed on Thursday by PT leader Krishnasamy and DMK Leader Karunanidhi.
Currently, 58 seats have been allotted to the allies, comprising 41 to Congress, 5 to IUML, 5 to MMK.
N R Dhanapalan's Perunthalaivar Makkal Katchi, Pon Kumar's TN Peasants and Workers Party and former IAS officer Sivakami's Samuga Samathuva Padai have got one seat each from DMK. These parties will be contesting under the DMK symbol - rising sun.
DMK is left with 176 seats, but more smaller parties are expected to join the alliance.