Following a legal apprenticeship with prominent Lebanese lawyers Edmond Gaspard and Yusuf al-Sawda, he established Mallat law offices in 1949. As a lawyer, he defended celebrated cases in Lebanese modern advocacy, winning landmark judicial victories on behalf of the Vatican and the Beirut Maronite Church. In 1972, he was elected president of the Beirut bar, and founded the first Arab Organization for Human Rights in 1974, together with prominent Arab lawyers like Abderrahmane Youssoufi (Arabic عبد الرحمن اليوسفي), a prisoner of conscience and later prime minister of Morocco.