Allen & Overy's (A&O's) Vietnam managing partner Dao Nguyen has left the firm, to be replaced by project finance and ex-Tokyo partner Adam Moncrieff.

Nguyen, who was previously Vietnam managing partner at Mayer Brown JSM, helped launch A&O's bases in Hanoi and Ho Chi Minh City after joining the magic circle firm in August 2012.

Specialising in corporate, banking, real estate and energy, Nguyen regularly advised developers and the Vietnamese government on significant project finance transactions, while acting for foreign companies on their investment into Vietnam.

Last year she represented Vietnamese-American investor Henry Nguyen on the expansion of the McDonalds food brand into the country, Nguyen having been nominated as the firm's franchise partner there.

Moncrieff, who relocated to Vietnam from A&O's Tokyo office in 2012, has been appointed as the firm's new country head.

Based in Ho Chi Minh City and focusing on banking, project finance and restructurings, he will work alongside A&O's other Vietnam partner Tran Anh Duc, who joined as Hanoi office manager and co-head of banking and corporate in December, from local firm Vilaf.

The firm now has two partners on the ground and approximately 15 associates.

Vietnam remains a small market for international law firms, with major players including just A&O, Baker & McKenzie, Freshfields Bruckhaus Deringer, Mayer Brown JSM, Duane Morris and Allens, as well as some Asian firms such as Japanese outfit Nishimura & Asahi, Singapore firm Rajah & Tann and Korea's Yulchon.

A&O is understood to be among the most successful foreign outfits in the country, with key mandates including the $5bn financing for the $9bn Nghi Son Refinery and Petrochemical Project – where it advised the export credit agencies and commercial lenders. Nguyen was the lead partner.

Clifford Chance also had offices in the country in the 1990s, which it closed in the year 2000 due a lack of lawyers ready to take over the business.

Related: Foreign law firms in Vietnam face pushback from local practices