Simpson Thacher & Bartlett has announced plans to open an office in Seoul.

The firm said in a statement it will open in the South Korean capital “as soon as practicable in 2012.” The announcement follows the ratification of a trade deal between the U.S. and Korea, the passage of which opens the way for U.S. firms to apply to enter Korea’s legal market from January.

New York partner Youngjin Sohn will relocate to Seoul along with several associates from the firm’s Hong Kong office.

Korea will be the fourth Asian location for Simpson Thacher, which already has offices in Hong Kong, Beijing, and Tokyo. The firm is among the market leaders for Korea work, and has recently acted on deals such as the initial public offerings of Samsung Life Insurance Co. and Korea Life Insurance Co. in 2010, raising $4.4 billion and $1.6 billion, resepectively. Simpson Thacher more recently acted for Korea’s Shinhan Bank on a $700 million notes issue, in December 2010.

Cleary Gottlieb Steen & Hamilton announced last month it will open an office in Seoul, while Sheppard, Mullin, Richter & Hampton followed suit last week. Paul Hastings has also said it wants to be among the first firms to enter the Korea market. McDermott Will & Emery and Ropes & Gray have also said they are considering opening offices in Korea.

British firms are also allowed to open offices in Korea following the passage of a free trade agreement between the EU and Korea in July. However, none has yet announced the opening of a Seoul office.