Theodard was uncle to his successor Lambert of Maastricht, and therefore brother or brother-in-law to Robert II, Lord Chancellor of France.

When Remaclus became bishop of Tongeren-Maastricht in around 653, Theodard succeeded him as abbot of the double monastery of Stavelot-Malmedy.

[2] His biographers describe him as a cheerful and likeable person who performed his role as bishop with great energy and pastoral care.

[3] He was murdered, probably c.670, while on a journey through the forest of Bienwald near Speyer, on his way to seek justice from Childeric II of Austrasia in a legal dispute regarding Frankish nobles plundering the diocese.

At first buried at the scene in Rülzheim, his body was later transferred to Liege by his nephew and successor, Lambert of Maastricht.