In 1946, al-Siba'i founded a Syrian branch of the Muslim Brotherhood, leading it through several parliamentary campaigns. After the United Arab Republic was formed in 1958, Gamal Nasser outlawed the Muslim Brotherhood and arrested hundreds of members. Joining the underground, Siba'i supported the 1961 coup ending the UAR. However, the Ba'ath government which came to power in 1963 again outlawed the Muslim Brotherhood, and banned many of Siba'i's works.