The development comes days after the party's humiliating defeat in the Madhya Pradesh Assembly polls, where the Congress, led by Nath, failed to replace the BJP government.
The two tribal dominated divisions of Surguja and Bastar having 26 assembly seats that contributed hugely to the Congress' landslide victory in Chhattisgarh in 2018 have swung to the Bharatiya Janata Party this time.
Congress's Devti Karma won the bypoll for the seat, reserved for Scheduled Tribes, by a margin of 11,192 votes, a poll official said.
The party renominated Shashi Tharoor from the Thiruvananthapuram seat.
The Congress has pinned its hopes on many of the old-timers and also given representation to some new faces in its first list of candidates announced for the Chhattisgarh assembly polls scheduled next month.
It's a single phase polling in Mizoram while first phase of assembly elections is underway in Chhattisgarh.