From running a tea shop to assuming charge as Chief Minister of Tamil Nadu twice, his political journey has been full of unexpected twists. He started his political career as a Chairman of Periyakulam Municipality from 1996 to 2001. In 2001, He was elected to the assembly from Periyakulam. After entering into the good books of Jayalalithaa, he became the Revenue Minister in 2001. In September 2001, he became the 14thChief Minister as an interim arrangement, after Jaya was forced to step down following a legal tangle.

His tenure lasted for only six months from September 21, 2001 to March 1, 2002 as he quit and paved the way for Jayalalithaa being sworn in again after the Supreme Court overturned her conviction and she won a by-election from Andipatti assembly in Theni district. He then became the Minister for Public Works, Prohibition and Excise. He was also entrusted with the Revenue Department's charge between 2003-2006. 

When the AIADMK was routed by DMK in the 2006 assembly elections, OPS was elected from Periyakulam assembly.  He became the leader of the AIADMK legislative party and Leader of the Opposition in Tamil Nadu legislative assembly. In 2011 assembly elections, he contested from the Bodinayakkanur assembly and won. He became the Finance Minister in Jayalalithaa's government.

OPS was again entrusted with the responsibility of being the 18th Chief Minister of Tamil Nadu on September 29, 2014 when Jayalalithaa was convicted in the disproportionate assets case. On May 22, 2015, he resigned as Chief Minister and Jayalalithaa was sworn in again after the Karnataka High Court acquitted her in the case. He was holding the Finance and Public Works Department portfolios till then.