The EC certified the status of Nirand Praditkul as a new appointed senator, replacing Prajit Rojanapruek.
Prajit was disqualified as a senator because he failed to exercise his right in the latest election.
EC secretary-general Phuchong Nutrawong said the EC would issue a certification for Nirand to present when he reports to work at the Senate.
Nirand, 68, was nominated for the position by the NACC. He resigned as a specialist working for the Constitution Court president on September 1.