This will come as a big surprise to many Nigerians, who had assumed that the Nigerian government had backed down following months of negotiations, says the BBC's Nduka Orjinmo in Abuja.
Nigeria suspended the social media firm last June after it deleted a tweet by President Muhammadu Buhari.
It accused Twitter of siding with secessionists.
Before ending the ban, the Nigerian government insisted that Twitter:
Register in Nigeria
Appoint a designated country representative
Comply with tax obligations in Nigeria
Enrol Nigeria in its portal for direct communications between government officials and Twitter to manage prohibited content that violates Twitter community rules
Act with a respectful acknowledgement of Nigerian laws
Twitter has not officially commented on what it has done to be allowed to work in Nigeria again but tweeted that it was "pleased" to be restored in the country and was "deeply committed to Nigeria".