Nigeria Becomes a Republic

In 1963 Nigeria adopted a new constitution and became a republic within the Commonwealth, ending the British monarch's role as head of state. According to the Library of Congress country study, the change called for no practical alteration of the constitutional system: a president, elected for five years by a joint session of parliament, replaced the Crown as the symbol of national sovereignty. Nnamdi Azikiwe, who had been governor-general, became the first president. Wikipedia notes that the Westminster system was kept, so that the president's powers were largely ceremonial and Abubakar Tafawa Balewa remained prime minister.

Nigeria became independent in 1960 as a Commonwealth realm, with Queen Elizabeth II as head of state, represented by a governor-general (Wikipedia). Becoming a republic within the Commonwealth replaced the Crown with a Nigerian head of state, but, as the Library of Congress country study notes, it called for no practical change in the constitutional system.

The change came in the middle of the crises of the First Republic. In 1962 the Action Group, the governing party of the Western Region, split between Obafemi Awolowo and Samuel Akintola; rioting followed, the federal government declared a state of emergency in the region, and Awolowo and others were later convicted of treason. In 1963 the creation of a Midwestern Region, carved out of the Western Region, was confirmed by plebiscite, and the census of 1962–63, which decided each region's share of seats, was bitterly disputed (country study).

The republican constitution kept the parliamentary system, so that real power remained with Prime Minister Abubakar Tafawa Balewa and the regional governments. The tensions of these years, over the census, the Western Region and the federal election of December 1964, led to the military coup of January 1966, which ended the First Republic (country study; Wikipedia).