According to the author himself Kugane Naruyama, volume 17 of the light novel Overlord , will conclude the series. This volume is scheduled for release on March 12th.
The author had previously hinted on his Twitter that he intended to finish the work in volume 17.
Overlord also received a anime adaptation successful 2015, with the first season consisting of 13 episodes.
All three seasons are officially available on Crunchyrollhas already been confirmed a fourth season
Source: ANN