Nearly 1,000 people, most of them children, have been affected by the outbreak which was first detected just over a month ago, the UN's Office for the Coordination of Humanitarian Aid (OCHA) said.
At least 50 of the cases were detected in Maradi city itself, OCHA said.
The first three cases were admitted to hospital in N'Yelwa at the beginning of July, with the number growing to 993 cases by August 7, OCHA said. The figure includes the 13 dead.
But Niger's Health Minister Iliassou Maïnassara told local media the government's rapid response had helped "rein in" the outbreak, along with help from the World Health Organization, UNICEF and Doctors Without Borders.
"The situation is under control and monitoring is being stepped up," said the minister, who visited Madarounfa, the area worst hit by the outbreak.
Cholera is caused by a bacterium transmitted through contaminated food or drinking water. It causes acute diarrhoea, with children particularly at risk.
Experts are concerned the highly-contagious disease could spread further following flooding caused by heavy rain in the infected area.