In the most competitive presidential election since the end of military rule, millions of Nigerians will cast their ballots.
Two parties, the ruling APC and the PDP, have controlled Africa's most populous nation since 1999.
The Labour Party's Peter Obi, who is supported by many young people, is a strong challenger this time around as a third-party candidate.
After serving two consecutive four-year terms, the current president, Muhammadu Buhari, is resigning.
Bola Tinubu, a former governor of Lagos, is running for his All Progressives Congress (APC), while Atiku Abubakar, a former vice president, is running for the Peoples Democratic Party (PDP), which is the main opposition force. There are a total of 18 candidates running for president.
The run-up to the election has been overshadowed by a cash crunch brought on by a failed attempt to redesign the currency, which has caused widespread chaos at banks and ATMs as desperate people tried to access their money.
The introduction of the new notes was made in an effort to combat vote-buying and inflation. A House of Representatives member was detained on the night before the election with nearly $500,000 (£419,000) in cash and a list of recipients, according to the police.
Regardless of who wins, they will have to deal with the new currency, a failing economy, high youth unemployment, and pervasive insecurity that resulted in 10,000 fatalities last year.
The parliamentary election in the southeast Enugu East constituency was postponed following the Wednesday murder of a senatorial candidate by suspected Ipob separatist gunmen.
A third of the 87 million eligible voters are under 35, so the election has attracted a lot of interest from young people and first-time voters, which could result in a higher voter turnout than the 35 percent seen in 2019.
First-time voter Blessing Ememumodak, 19, told the BBC in Lagos, "It is my responsibility and I have seen how important it is to vote.".
Following his May 2018 joining of the Labour Party, Mr. Obi, 61, hopes to end Nigeria's two-party system.
Although he had previously been a member of the PDP, some young people in Nigeria, particularly those in the south, view him as a relatively new face and give him ardent support.
From 2006 to 2014, the successful businessman presided over the state of Anambra in the southeast. The "OBIdients," who support him, claim he is the only candidate with integrity, but his detractors contend that supporting Obi is pointless because he is not likely to win.
Instead, the PDP, which ruled until 2015, is urging Nigerians to support 76-year-old Atiku Abubakar, the only significant candidate from the region's predominantly Muslim north.
He has previously made five unsuccessful runs for the presidency. Despite his denials, he has been the target of persistent allegations of cronyism and corruption.
Having served as a top official, vice president, and well-known businessman, he has spent the majority of his career in positions of authority.
Since the APC has presided over a period of economic hardship and escalating insecurity, the majority of people view the election as a referendum on its leadership.
Its candidate, 70-year-old Bola Ahmed Tinubu, is credited with developing Lagos, Nigeria's commercial center, during his two terms as governor from 2003 to 2007.
In the south-west region, where he has significant influence, he is regarded as a political godfather. However, like Mr. Abubakar, he has long been the target of allegations of corruption and poor health, both of which he vigorously denies.
Any person in line before it closes at 14:30 will be able to cast a ballot. Voting is anticipated to start at 8:00 local time (07:30 GMT).
In addition, there are elections for 109 federal senators, 360 members of the house of representatives, and for governors in March.
The Independent National Electoral Commission (Inec) has pledged to hold free and fair elections and has dismissed talk of delaying the vote due to unrest in some areas of the nation and a cash shortage that some feared might hamper the commission's preparations.
The Bimodal Voter Accreditation System (BVAS), a facial recognition and fingerprinting system, will be used for the first time by Inec to conduct national elections. This system is thought to increase transparency by making it more difficult for politicians to rig the system.
Final results were announced three days after voting in the previous two elections, but this time they might be released earlier thanks to BVAS, which also uploads vote results directly from the polls to the Inec website.
For a candidate to be declared the winner, they must receive the most votes and 25% of the total ballots cast in at least two-thirds of the country's 36 states.
If no one succeeds in doing that, a run-off election will be held in 21 days, a first in Nigerian history.