An influential artist in royal courts across Europe, he was made Honorary Designer of His Majesty The King of the Belgians by Leopold I of Belgium.

Diez also served in a political role at court, and was appointed as a Privy Councillor by Heinrich LXVII, Prince Reuss Younger Line.

[3] In 1832 Diez was brought to the royal court in Meiningen by Georg II, Duke of Saxe-Meiningen to work as a painter.

In 1858 Diez was appointed as a Geheimrat, or privy councilor, by Heinrich LXVII, Prince Reuss Younger Line.

Some of his notable works include portraits of Karl August Varnhagen von Ense, Bernhard II, Duke of Saxe-Meiningen, Christian Daniel Rauch, Leopold I of Belgium, and Ludwig Bechstein.