Hesse-Nassau was created as a consequence of the Austro-Prussian War of 1866 by combining the previously independent Hesse-Kassel (or Hesse-Cassel), the Duchy of Nassau, the Free City of Frankfurt, areas gained from the Kingdom of Bavaria, and areas gained from the Grand Duchy of Hesse (including part of the former Landgraviate of Hesse-Homburg from Hesse-Darmstadt).

These regions were combined to form the province Hesse-Nassau in 1868 with its capital in Kassel and redivided into two administrative regions: Kassel and Wiesbaden.

In 1935, the Nazi government de facto abolished all states, so the provinces held little meaning.

The Oberpräsident administered the province with the assistance of a Prussian government-appointed provincial council.

The Dutch royal house originates from the Duchy of Nassau.