“Nigeria is now free of Ebola,” WHO Representative, Rui Gama Vaz, told a news conference in the capital Abuja.
“This is a spectacular success story,” he added.
Nigeria won praise for its swift response after a Liberian diplomat, Patrick Sawyer, brought the disease there in July.
With 60% survival rate, Nigeria is the most effective in dealing with the virus.
Nigeria declared a national public health emergency and Mr Sawyer later died of the disease, followed by seven Nigerians.
These included Dr Ameyo Stella Adadevoh, who diagnosed Mr Sawyer and is credited with helping to contain the outbreak at its source.
The outbreak has killed more than 4,500 people in West Africa, mostly in Liberia, Guinea, and Sierra Leone.
An estimated 70% of those infected have died in those countries.
The WHO officially declared Senegal Ebola-free on Friday.
Meanwhile, European Union foreign ministers are meeting in Luxembourg to discuss how to strengthen their response to the threat posed by Ebola.
European countries have committed more than 500m euros (£400m; $600m) but the UK is pressing to double that amount.