Police and the British High Commission named the woman as Faye Mooney, 29, and said they were aware of an incident which took place at a holiday resort on Friday but would not speculate on a motive, Sky News reported.
Her next of kin have been informed.
The Briton was working in Nigeria as a communications specialist for aid group Mercy Corps and was one of 12 tourists travelling to the northern city of Kaduna from Lagos, police said.
Police said Ms. Mooney, who worked in the West African nation for nearly two years, had been attending a party before the incident.
In a statement, Mercy Corps said it was "utterly heartbroken" by the killing.
"Faye was a dedicated and passionate communications and learning specialist who had worked with Mercy Corps for almost two years, devoting her time to making a difference in Nigeria, supporting our teams and the communities we work with to tell their stories of impact, and leading efforts to counter hate speech and violence.
"A graduate of University College London and the London School of Economics who had taught in Iraq and worked in Kosovo to combat human trafficking, Faye was deeply committed to fostering cross-cultural collaboration and was an inspiration to us all.
"We extend our deepest sympathy to those who have been affected by this senseless tragedy, including her family, friends and all of our team members in Nigeria who knew her and loved her."
A Kaduna state police spokesman said, "Some suspected kidnappers armed with dangerous weapons gained entry into a recreational resort called Kajuru Castle in Kajuru local government area shooting sporadically and in the process shot dead two persons, including an expatriate lady, and took away three others."
Officers have not yet named the other person killed in the incident.
No individuals or groups have said they are behind the killing and police are yet to identify the kidnappers.
Northern Nigeria has been dealing with a Boko Haram and Daesh insurgency and clashes between farmers and herders, in which hundreds have died.
Kaduna has seen a spate of kidnappings by armed men in recent months.
In a statement, the British High Commission said, "We are aware of the tragic incident involving the death of a British national in Kaduna State on Friday.
"The next-of-kin has been notified.
"The British High Commission offers our most profound sympathies and condolences to the families and friends at this difficult time."