Simpson Thacher & Bartlett will close its Seoul office by the end of the year, becoming the first major global firm to pull out of South Korea since the country opened up its legal market in 2012.

The US firm had already relocated its Korea practice back to Hong Kong earlier this year.

Corporate partner and head of the base, Youngjin Sohn, will leave the firm following the office closure. Sohn, who relocated from New York to open the office six years ago, is the only lawyer currently in the base after the departures of corporate associates John Hahn earlier this year and Iksoo Kim in 2017.

Simpson Thacher's Korean practice head Jin Hyuk Park said the firm is shutting the Seoul office for strategic reasons. He added: "We continue to focus on and serve our clients who are active in Korea from our Hong Kong office, where we have five Korean-speaking lawyers. We have many other Korean-speaking lawyers in our New York and other offices who support our Korea practice."

The firm was among the first batch of US players to launch physical presences in Seoul in 2012, following the ratification of the US-Korea free trade agreement (FTA). Before foreign firms were allowed to physically launch in Seoul, Simpson Thacher – like other stronger Korea players such as Cleary Gottlieb Steen & Hamilton and Paul Hastings – based its Korea practice out of the Hong Kong office. The firm maintained a Korea-focused team in Hong Kong after launching a Seoul office, and Park has been based in Hong Kong since then.

Simpson Thacher's impending exit will leave 28 foreign firms – 21 of which are US firms – in Seoul giving non-Korean law advice, although this number is set to be boosted by the arrival of Shearman & Sterling, which has has confirmed plans for a launch, pending regulatory clearance.

The New York-based firm has applied to set up a foreign legal consultant office in Seoul and is waiting for approval from the South Korean Ministry of Justice. Anna Chung, a projects partner in Singapore, is expected to relocate to head the Seoul office. It will consist of three lawyers focusing on outbound projects work, as well as working with lawyers in other offices on Korea-related antitrust and arbitration work.

Chung, who joined Shearman's London office in 2006 from Australian firm Corrs Chambers Westgarth, made partner at the firm last year. She also worked in Shearman's Shanghai office from 2008 to 2011.

Last year, the firm advised the lenders and export credit agency Korea Trade Insurance Corporation on the financing of a $545m coal power plant in Indonesia. The deal was led by a Singapore-based projects team that included William McCormack, the firm's Asia regional managing partner, and Chung.

The office in Seoul will be the US firm's sixth in Asia, alongside Hong Kong, Tokyo, Beijing, Singapore and Shanghai.

Latham & Watkins, which opened a Seoul office in 2016, was the most recent heavyweight firm to enter Korea.

Foreign firms were first allowed to offer local law advice once the FTAs with firms' home countries reached their fifth year. But to the disappointment of many international firms, the country's legislature passed a revision to the Foreign Legal Consultant Act in February, rescinding the promise of fully opening up the market. Instead, it only allowed restrictive joint ventures between established local practices and foreign firms. So far, none of the 28 foreign firms have established such joint ventures.