Assembly Secretary-cum-Returning Officer A K Sarangi declared Swain's election as neither Congress nor BJP fielded any candidate for the poll.
The Rajya Sabha seat had been vacant since July 25, 2015 following the death of Kalpataru Das. Das was elected to the Upper House in April 2014.
Swain on December 3 had filed two sets of nomination papers at the office of Assembly secretary. Today was the last date of withdrawal of nominations.
As there was no contestant against Swain, he was declared elected unopposed to Rajya Sabha, Sarangi said.