Speaker Nabam Rebia administered the oath of office and secrecy to Karbak at the Nokmey Namati Hall of the Assembly secretariat at Naharlagun.
Karbak won the bye-poll held on February 13 last by a margin of 119 votes defeating his nearest rival Bai Gadi of the BJP.
Bye-election to the constituency was necessitated following sudden demise of former Chief Minister Jarbom Gamlin at a Gurgaon hospital on November 30 last year.