Should the outcome require a second round, 6 July is set for the runoff, the decree said, adding that the armed and security forces will vote the day before the election, a usual measure designed to free them so that they can maintain order on polling day.
The election campaign will start on June 7 and will last 14 days.
There are five potential candidates namely former Defence Minister Mohamed Ould Ghazouani, former Prime Minister Sidi Mohamed Ould Boubacar, anti-slavery activist Biram Dah Abeid, Mohamed Ould Maouloud and Hamidou Baba Kane.
The list of presidential candidates could be extended since the deadline for submitting applications expires on May 8, according to the decree.
The final list of candidates will be made public on May 22.