Sunil was formally admitted into the TDP by the party national president and Chief Minister N Chandrababu Naidu.
With this, the total number of legislators who switched sides from YSRC to TDP increased to nine.
Two YSRC MLAs from East Godavari district have already quit the party and announced their decision to join the TDP. Jyothula Nehru and V Subba Rao will complete the formality in the next couple of days.
With the defection of these many MLAs, the strength of the lone Opposition in the 176-member Legislative Assembly fell to 56.
The TDP successfully thwarted YSRC president Y S Jaganmohan Reddy's attempts to get the defected MLAs disqualified by issuing a whip in the Budget session of the Assembly last month.