Padmaraju said he joined the TDP to take part in the development of the residuary state under Chief Minister Chandrababu Naidu's leadership.
Padmaraju, who hails from West Godavari district, had become an official spokesman of Andhra Congress after the state's division last year.
Congress' strength in the 50-member Upper House has now been reduced to 10 with the defection of its members.
Nine Council seats are vacant currently and eight new ones are to be created shortly to rectify an anomaly caused during the state bifurcation.