Vallendar is first mentioned around 830–840 AD as the property of the Archbishop of Trier; it was probably, however, of Celtic origin and a lot older (700–600 BC).

In 1232 the Count of Sayn took possession of the land and began building a castle at the northern edge of the town in 1240.

Today the Lion of Sayn and the Cross of Trier are evidence of this history in Vallendar's coat of arms.

A rich business life is the reason why Frederick William IV of Prussia granted town rights to Vallendar in 1856.

Today Vallendar's appearance is influenced mostly by the internationally renowned Schönstatt and the WHU – Otto Beisheim School of Management and its students.