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".
But the BBC understands it has largely agreed to the government demands.
The move allows millions of people in Africa's most populous nation to use the platform again.
Many Nigerians had continued to access the site after the suspension using virtual private networks (VPNs) but most corporate organisations, including many media outfits, had obeyed the government's order.
Analysts believe the ban has cost the Nigerian economy millions of dollars, especially the small businesses which use the platform to reach their customers.
The move last year by Nigeria's government sparked an international outcry over freedom of speech.
The social media company's decision to register itself in the country showed it was committed to Nigeria, the country's information technology development agency said.
The government had ordered internet providers to block Twitter, alleging it was being used to undermine "Nigeria's corporate existence" through the spreading of fake news that could potentially have "violent consequences".
This came after Twitter removed President Buhari's post referring to the 1967-70 Nigerian Civil War and to treating "those misbehaving today" in "the language they will understand".
Twitter is popular with many Nigerians, and the platform has been used as a mobilising tool. Activists used it to rally support during protests against police brutality under the hashtag #EndSars, which gained global attention.
Despite the ban many Nigerians continued to tweet and some are now taking time to recognise the VPNs that enabled them to do so.
User Ugegbe tweeted that she didn't want to delete her VPN, as it would feel like a betrayal.