On 25 February, Nigeria holds its elections for president, house, and senate. The country uses single-seat plurality elections, but with an important qualification in the case of the federal presidency. The winner of that contest must have not only a nationwide plurality of votes, but also meet a “distribution” requirement: earn at least a quarter of the vote in at least two thirds of the federal entities (consisting of 36 states and a capital territory).
If the first-round plurality candidate fails to meet the distribution qualification, then there is a runoff. The two candidates in a runoff would be the plurality candidate and the other candidate who wins the most states with a majority of the vote. Note that if there are three or more serious candidates, with regional bases, the runoff opponent might not be the one with the second highest votes in the first round.
Nigeria this year has precisely the situation that could lead to a runoff and possibly not with the top-two candidates: There are at least three candidates who might be considered “serious” and all exhibit Nigeria’s typical tendency towards regional concentration of support. See Africa Elects. Nigeria has not previously had a runoff.
Polling is apparently sparse, but shows Peter Obi of the Labour Party (LP) in the lead–some recent polls show him far ahead. I am not sure how reliable Nigerian polls are, let alone whether they effectively capture state-by-state trends. The next two candidates after Obi appear close in polling: Bola Tinubu (All Progressive Congress, APC) and Atiku Abubakar (Peoples Democratic Party, PDP). A fourth candidate, Rabiu Kwankwaso of the New Nigeria Peoples Party (NNPP) also has regionally concentrated support. Given the distribution requirement, even a candidate with little chance of winning might deprive a more nationally popular candidate of 25% of the vote in some states or of a majority in enough states to affect runoff qualifications should there be a second round.
The APC is the incumbent president’s party, and the PDP has provided the winning ticket in various past elections (including its presidential candidate this year as vice president in the past). Obi was the PDP’s vice presidential candidate in the last national election, in 2019, with Abubakar at the top of the ticket.
As far as congress is concerned, at the 2019 election the APC won 202 seats and the PDP 126 in the House of Representatives, which has 360 seats. In the 109-seat Senate, the APC won 63 and the PDP 44. It seems likely that this year’s results will be more fragmented, but given the use of single-seat plurality in both houses, obviously it depends entirely on the parties’ relative regional concentration in the voting.
Nigeria uses a pure presidential system.