Sabarinath (Congress), son of late Speaker G Karthikeyan, filed papers before the returning officer. KPCC President V M Sudheeran accompanied Sabarinath.
BJP State President V Muraleedharan and other senior state party leaders accompanied Rajagopal when he filed the papers.
Former speaker, M Vijaykumar (CPI-M), the LDF candidate, had filed his nomination on June 8.
The election was necessitate following the death of Karthikeyan, who represented the constituency.