Lagos - Amnesty International urged President Goodluck Jonathan to reject a bill that would outlaw gay marriage and crackdown on gay rights after lawmakers approved a final version for his signature.
The key elements of Nigeria's anti-homosexuality legislation, which also criminalises public displays of affection between same sex couples, had cleared the upper and lower houses of parliament in May.
But there were minor differences between the drafts passed by the two legislative bodies.
Those discrepancies were resolved on Tuesday and the bill is now ready for Jonathan's signature.
"This discriminatory bill, which not only criminalises same-sex marriage but also makes public displays of affection and even socialising in the lesbian, gay, bisexual, transgender and inter-sex community illegal, must be rejected by the President," said Aster van Kregten, Amnesty International's Africa Deputy Director.
"If the President signs the bill into law it would make Nigeria one of the least tolerant societies in the world and have catastrophic consequences for the country's LGBTI community and human rights organisations."
Uganda's parliament on Friday adopted its own anti-gay bill that calls for repeat offenders to be jailed for life.
Like the Nigerian bill, it will only come into force if the country's President Yoweri Museveni signs it.
Both pieces of legislation have been widely condemned by rights groups and world leaders, including in the US and Britain.
Nigeria is seen as being less susceptible to pressure from Western governments because, as Africa's top oil producer, it receives very little foreign aid.
Under Nigeria's bill, anyone who enters into a same-marriage or "civil union" can be sentenced to 14 years in prison.
It also says "any person who registers, operates or participates in gay clubs, societies and organisations or directly or indirectly makes a public show of same-sex amorous relationship commits an offence and shall be liable to a term of 10 years imprisonment."
Jonathan's intentions regarding the bill are not clear.