Fifty-eight newly elected members of the Meghalaya assembly took oath on Monday with pro-tem speaker Timothy D Shira administering the oath of office and secrecy to them.
NPP head and outgoing chief minister Conrad K Sangma was present at the ceremony.
Meghalaya has 60 assembly seats but polling in the Sohiong constituency was adjourned after the demise of UDP nominee H D R Lyngdoh.
Shira, the MLA of Resubelpara, was sworn in, as the pro-tem speaker of the assembly, by Governor Phagu Chauhan at the Raj Bhavan on March 4.
Among senior MLAs who took oath as members of the House included Sangma and Prestone Tynsong of the NPP, TMC's Mukul Sangma, and Metbah Lyngdoh of the UDP.
A special session of the assembly was convened for the swearing-in ceremony of the newly elected MLAs.
Prime Minister Narendra Modi is likely to attend the swearing-in ceremony of the NPP-led government, scheduled on Wednesday.
The House will again meet on March 9 for the election of the speaker.
The NPP-led alliance with 32 MLAs has staked claim to form the next government in the northeastern state, under the leadership of Conrad K Sangma.
The NPP won 26 seats in the recently concluded elections, while its ally, the BJP, won only two assembly segments.
Two Hill State People's Democratic Party MLAs, who have won the elections, have also pledged their support to the NPP-BJP coalition, along with two other Independent legislators.
Two major regional parties the United Democratic Party (UDP) and the People's Democratic Front (PDF) on March 5 extended their support to the NPP-led alliance, increasing the number of MLAs backing the Sangma-led coalition to 45.