1998: Mamata Banerjee and Mukul Roy leave Congress over differences and form the All India Trinamool Congress. Quickly rose to prominence, winning seven seats in the 1998 Lok Sabha Elections, getting into the BJP-led NDA.
1999: Wins eight seats in the 1999 Lok Sabha elections in alliance with BJP, gaining significant traction among leaders and the people of West Bengal. A part of the NDA, Mamata Banerjee becomes the Railway Minister for the first time.
2000: TMC wins the Kolkata Municipal Corporation Elections in alliance with BJP, and the support of the Indian National Congress, ending Left Front’s fifteen year-hold on the KMC elections.
2001: The party wins an impressive 60 seats in the 2001 West Bengal Assembly elections, having ended ties with NDA and allied with the Congress, becoming the primary opposition in the state. It marks the first time since 1971, no party is able to secure an absolute majority and the first time since 1977, that the CPIM fail to secure a majority of its own.
2004: TMC underperforms at the 2004 Lok Sabha elections, under the NDA banner, winning a meagre two out of the 31 seats contested across West Bengal, Meghalaya and Tripura. Having joined the NDA back in 2003, Mamata Banerjee and close aide Sudip Banerjee are made part of the cabinet, with Banerjee taking the Coal and Mines portfolio.
2005: TMC loses crucial Kolkata civic polls, with sitting Mayor and credible TMC face Subrata Mukherjee defecting to NCP ahead of the polls. TMC protests intensify against CPIM’s industrial projects including handing over farmland in Howrah to Salim group.