At the age of 21, Korn began his career as an investment banker in 1985, his first role being in asset management for SG Warburg.

Three years later in 1988, Korn founded JF Thanakom Securities, becoming the youngest head of a Thai investment bank at the time.

In early 2006, Korn had an important role in scrutinizing the sales of the shares of Shin Corp owned by the Shinawatra and Damapong families.

At the time, the Shinawatra family's sales of the Shin Corps shares were criticized for tax evasion and conflict of interest.

[2] At the 2007 general election, Korn was re-elected as a Bangkok MP for the Bangkholam, Yannawa, Khlong Toey and Wattana districts.

Korn's tenure was focused on responding to the Global Financial Crisis, which had begun in the United States of America.

[4][5] As then Chair of the ASEAN Finance Ministers' meetings in 2009, Korn helped create the Chiang Mai Initiative Multilateralization (CMIM), a regional foreign reserve pool to remedy currency flow shortages.

In January 2010, Korn was named "Finance Minister of the Year 2010", both globally and for the Asia Pacific region by The Banker magazine of the Financial Times.

The magazine complimented the Thai minister on his "financial management skills as he assumed the finance ministerial position in Thailand amid the economic stagnation".

[10] In August 2014, Korn established Kaset Khem Kaeng, a non-profit with a mission to help small farmers practice sustainable farming and receive fair compensation for their produce.

In September 2022, Korn announced in a press conference that he would be joining forces with Suwat Liptapallop, a former deputy prime minister and the chairman of the Chart Pattana Party.

[13] Korn announced that under his leadership, Chart Pattana Kla would focus on economic policies at the next general election.

Siang's grandson, Jard Sae Sol commissioned the construction of a Chinese-styled house known as Sou Heng Tai in Talad Noi during the early-19th century.