Abubakar, who has already run for the presidency four times, has amassed a huge fortune in the import-export business, as well as oil, agriculture and telecommunications.
Nigerian President Muhammadu Buhari will run for re-election in February 2019 against former vice president Atiku Abubakar, a Muslim from the country's north who was nominated on Sunday as the main opposition party's poll contender.
Buhari, a 75-year-old former military ruler, was the sole candidate for his ruling All Progressives Congress (APC) party, so his confirmation by some 7,000 delegates gathered in the capital Abuja was a mere formality on Saturday.
The APC swept to power in 2015 with the first opposition victory at the ballot box in the country's history.
But next year's presidential race appears to have tightened in recent months with the APC hit by a wave of defections over Buhari's leadership style.
On Sunday, delegates to a convention of the former ruling People's Democratic Party (PDP), nominated Abubakar, 71, as his challenger for next year's poll.
The politician and business tycoon has made four previous bids for the top job in Nigeria, Africa's most populous nation.
AFP