The 1,000-mile (1,600-kilometer) border was closed after West African leaders imposed sanctions on Niger following a coup that ousted president Mohamed Bazoum.
Last month the Economic Community of West African States (ECOWAS) decided to lift the sanctions, but the border has remained closed on both sides.
Local AFP sources confirmed the frontier in the state of Katsina in northern Nigeria was still shut late on Wednesday.
A document by the Nigeria Immigration Service document dated Thursday instructed officials to "reopen their borders with immediate effect," in line with an ECOWAS decision and a directive issued by Nigerian President Bola Ahmed Tinubu the previous day.
Tinubu called for land and air borders to be reopened and asset freezes and travel and financial transaction bans and restrictions to be lifted.
Electricity supplies from Nigeria resumed at the start of March, putting an end to the power cuts that had hit Niger since the military came to power.
The West African Economic and Monetary Union has also lifted sanctions, which included freezing Niger's assets and suspending financial transactions.
The ECOWAS decision to lift sanctions signals a desire to renew dialogue with military regimes among its members after Mali, Niger and Burkina Faso announced their intention to leave the bloc.
ECOWAS imposed tough sanctions after Niger's coup in July last year, but the bloc's warning of military intervention fizzled out.
Nigeria Re-Opens Border with Neighboring Niger
LAGOS — Nigerian border officials were Thursday ordered to immediately reopen the frontier with Niger, closed since August following a coup that ushered in military rule.
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