Dietrich was a member of the noble von Horne family, who resided at Horneburg Castle (later name Harenburg Castle) northeast of the settlement of Westendorf, today called Bieste, north of Osnabrück.

[2] In 1376, the cathedral chapter of the Bishopric of Osnabrück elected Dietrich in episcopum et pastorem ecclesie Osnaburgensis, i.e. as the new bishop.

A conflict arose when Otto VI remanded that Dietrich should concentrate on the religious affairs of his diocese, leaving worldly power in his bishopric to the counts of Tecklenburg.

[3] Dietrich managed to reconquer several towns, including Vörden, during the course of this conflict.

[3][4] During his tenure there was also a dispute with the Order of Saint John, Commandry of Lage, who refused to pay taxes to the bishopric.