He was the eldest son of Johann Wilhelm, Duke of Saxe-Weimar and Dorothea Susanne of Simmern.

At the time of the death of his father (1573), Friedrich Wilhelm was still under age; for this, a tutelary government for the duchy was appointed.

The Dowager Duchess, Dorothea Susanne, could however not prevent the Elector Augustus of Saxony – from the Albertine line – from being designated as the regent in her place.

In Weimar on 5 May 1583 Friedrich Wilhelm married firstly with Sophie, daughter of Christoph, Duke of Württemberg.

They had six children: NB: This entry quotes German Wikipedia: de:Friedrich Wilhelm I.