The 20 lawmakers who quit the Trinamool Congress to join the Nationalist Citizens Party of India will mirror the hierarchy of their former party.
Kakoli Ghosh Dastidar, the face of the rebel MPs, said the earlier arrangement would continue.
Veteran MP Sudip Bandopadhyay will be the new floor leader of the NCPI, and Shatabdi Roy will be nominated as the deputy leader.
The merger has boosted the NCPI, taking its strength from 294 to 314 in the Lok Sabha.
Opposition lawmakers have criticized the defection, calling it a dismal state of affairs for Indian democracy.
