Johann Theodor was the son of Elector Maximilian II Emanuel of Bavaria and of his wife Theresa Kunegunda Sobieska (daughter of King John III Sobieski of Poland).

[1] On 9 September 1743 Johann Theodor was created a Cardinal-Priest by Pope Benedict XIV, but his name was reserved in pectore and was not announced until 17 January 1746.

Johann Theodor was known as a great hunter, patron of music (he played the violoncello) and theatre, and held a splendid court at Liège.

Asthmatic and tubercular, he gave into the advice of his doctor, a physician named Steppler (a German from Munich), who claimed that his sickness originated from coal vapours.

He was buried in Saint-Lambert Cathedral in Liège while his heart was placed in the Chapel of Grace in the Shrine of Our Lady of Altötting.