Mizoram Legislative Assembly Speaker Hiphei resigned from his post, the House as well as the Congress and joined the Bharatiya Janata Party just three weeks ahead of the assembly elections in the state.
Earlier, the seven-time Congress legislator submitted his resignation letter to Deputy Speaker R. Lalrinawma. He is the fifth Congress MLA to resign from the 40-member House since September.
Mizoram, the only state in the north-east under Congress rule, will go to the polls on November 28.
In Guwahati, convenor of the North East Democratic Alliance (NEDA) and BJP leader Himanta Biswa Sarma said Hiphei, 81, will join the saffron party in his presence in the Mizoram capital Aizawl.
"He is a very senior leader. His joining the saffron party will greatly strengthen the organisation," Sarma, who is also Assam finance minister, said.
The senior BJP leader, however, did not comment on whether the party will field Hiphei from any constituency in the forthcoming Assembly polls in the hill state.
The Congress had earlier named Hiphhei as its candidate for the Palak constituency, but replaced him with party general secretary K T Rokhaw last week following reports that he might move to the BJP.
Hiphei was elected to the Mizoram Assembly from Palak constituency in 2013. He won the state elections six times between 1972 and 1989 from Tuipang.