They would tender their resignation to the Assembly speaker on December 29 and be officially inducted into the NPP on January 4, he added.
"Me and my colleagues have lost faith in the Congress leadership. We are joining the NPP, which has proven to be more democratic," Lyngdoh told PTI.
State NPP chief W Kharlukhi told reporters that eight MLAs, including five from the ruling Congress, would be joining the party at a rally at the Polo grounds on January 4.
"All the MLAs have been assured of NPP tickets to contest from their respective constituencies," Kharlukhi said.
The other MLAs to be inducted into the NPP are -- Hopeful Bamon (Independent), Stephanson Mukhim (Independent) and Remington Pyngrope (United Democratic Party).
Polls are due in the north-eastern state early next year with the term of the current Assembly ending on March 6.