The Iraqi Regional Branch of the Ba'ath Party was established in 1951 or 1952. Some historians claim that the Iraqi Regional Branch was established by Abd ar Rahman ad Damin and Abd al Khaliq al Khudayri in 1947 after their return from the founding congress of the Ba'ath Party held in Damascus, Syria the same year. In another version, Fuad al-Rikabi established the Iraqi Regional Branch in 1948 with Sa'dun Hamadi, a Shia Muslim, but became secretary of the Regional Command in 1952.
The Iraqi Regional Branch was Arab nationalist and vague in its socialist orientation. Al-Rikabi, expelled from the party in 1961 for being a Nasserist, was an early follower of Michel Aflaq, the founder of Ba'athism. During the party's early days, members discussed topics regarding Arab nationalism, the social inequalities that had grown out of the British "Tribal Criminal and Civil Disputes Regulation," and the Iraqi Parliament's Law 28 of 1932 "Governing the Rights and Duties of Cultivators". By 1953, the party, led by al-Rikabi, was engaged in subversive activities against the government.
The party initially consisted of a majority of Shia Muslims, as al-Rikabi primarily recruited his friends and family, but it slowly became Sunni-dominated. The Ba'ath Party, and others of pan-Arab orientation, found it increasingly difficult to recruit Shia members within the party organisation. Most Shias saw pan-Arab as largely Sunni, since most Arabs are Sunni. As a result, more Shias joined the Iraqi Communist Party than the Ba'ath Party. In the mid-1950s, eight of 17 members of the Ba'ath leadership were Shia.
According to Talib Shabib, the Ba'ath foreign minister in the Ahmed Hassan al-Bakr government, the sectarian background of the leading Ba'ath members was considered of little importance because most Ba'athists did not know each other's sectarian denominations. Between 1952 and 1963, 54% of the members of the Ba'ath Regional Command were Shia Muslims, largely because of al-Rikabi's effective recruitment drive in Shia areas. Between 1963 and 1970, after al-Rikabi's resignation, Shia representation in the Regional Command had fallen to 14 percent. However, of the three factions within the Ba'ath Party, two out of three faction leaders were Shia.
By the end of 1951, the party had at least 50 members. With the collapse of the pan-Arabist United Arab Republic (UAR), several leading Ba'ath members, including al-Rikabi, resigned from the party in protest. In 1958, the year of the 14 July Revolution that overthrew the Hashemite monarchy, the Ba'ath Party had 300 members nationwide. General Abd al-Karim Qasim, the leader of the Free Officers Movement which overthrew the king, supported joining the UAR, but changed his position when he took power. Several members of the Free Officer Movement were also members of the Ba'ath Party. The Ba'ath Party considered the President of Egypt Gamal Abdel Nasser, the leader of the pan-Arab movement, to be the leader most likely to succeed, and supported Iraq's joining the union. Of the 16 members of Qasim's cabinet, 12 were Ba'ath Party members. However, the Ba'ath Party supported Qasim on the grounds that he would join Nasser's UAR.