He was administered the oath by Governor Syed Ahmed at the Raj Bhavan here.
Chief Minister Raghubar Das, Parliamentary Affairs Minister C P Singh, former Chief Minister Hemant Soren and several other dignitaries were present on the occasion.
The four-day Assembly session begins on January 6 when the newly elected MLAs will take oath.
BJP has nominated its MLA Dinesh Oraon for the post of Speaker. He appears set to win as the BJP/Ajsu alliance has 42 of the total 81 MLAs in the House.