From 2003 to 2011 he was the Secretary-General of the Securities and Exchange Commission of Thailand and Chairman of the ASEAN Capital Markets Forum (ACMF).

Other positions held by Thirachai Phuvanatnaranubala included member of the board of Experts for Interpretation of Tax Code, the Thai Institute of Directors, the Financial Institution Policy Board at the Bank of Thailand, the National Credit Bureau Co., Ltd. and the Insurance Commission.

Additionally, he served on various government agencies' committees to study and recommend on policy issues.

In December 2003, Thirachai was appointed Secretary-General of the Securities and Exchange Commission (SEC) of Thailand.

After her success in the 2011 general election, Pheu Thai Party leader Yingluck Shinawatra chose him for Finance Minister after Siam Commercial Bank Pcl Chairman Vichit Suraphongchai declined to accept the position.