On 1 October 1979 the Federal Military Government handed over to a civilian administration under President Shehu Shagari, NPN. The 1979 Constitution replaced the Westminster parliamentary system of the First Republic with an American-style executive presidential system — Nigeria's first.
Shagari had won the August 1979 election on the Supreme Court's '12⅔ states' interpretation in Awolowo v. Shagari (FCA/CA/95/79) — the most contested electoral arithmetic in Nigerian history before 2007. The Republic lasted four years and three months, ended by the 31 December 1983 coup.