Sukhdeo, also the Jharkhand PCC president, took the oath in the House on the penultimate day of the Winter Session, taking Congress' strength in the 82-member Assembly to seven.
He won the Lohardaga (ST) by-poll on December 14 after the seat fell vacant following disqualification of Ajsu leader Kamal Kishore Bhagat.
Kamal was convicted and sent to jail for five years in connection with a 1993 criminal case.