During his legal career and even during retirement and exile, he authored a number of books, including one entitled Vietnamese Civil Law.

He strongly opposed the fierce repressive measures of the Ngô Đình Diệm's government against Buddhism.

Mẫu was South Vietnam's ambassador to the United Kingdom, Belgium, and the Netherlands in the mid- to late 1960s.

Therefore, when General Dương Văn Minh became president, he was nominated for the post of Prime Minister of the Republic of Vietnam for the purpose of participating in negotiations to end the war.

Like General Dương Văn Minh, he was a moderate, supporting the policy of handing over the government to the Liberation Army.

After the situation stabilized, Mẫu was allowed to leave the country to immigrate to France in 1988 and settled there for the rest of his life.