Suparerk Auychai has banking and equity capital markets expertise and will join A&O's 26-lawyer Bangkok office.
Auychai was a partner at Norton Rose for two years, having been made up in 2005. Norton Rose is now left with just two partners in its Bangkok office, which is managed by corporate finance partner Phillip John, who founded the office in 2000.
Last year Auychai led advice to the underwriters on the Rayong Refinery Public Company's $720m (£390.47m) float on the Thailand Stock Exchange.
A&O Bangkok managing partner Simon Makison said: "As capital markets and banking transactions continue to develop in Thailand, Suparerk's knowledge of the regulatory environment in Thailand, and his understanding of how this impacts on domestic and international transactions, will further enhance our practice."