In the Middle Ages it was a prince-bishopric of the Holy Roman Empire, a de facto independent state ruled by the prince-bishop who had the ex officio title of count.

After the French Revolution, the last prince bishop, Cardinal Louis de Montmorency-Laval (1761-1802) fled and the old organization of the diocese was broken up.

With the Concordat of 1801 the diocese was re-established covering the departments of Moselle, Ardennes, and Forêts, and was put under the Archdiocese of Besançon.

[citation needed] When the 1905 French law on the Separation of the Churches and the State was enacted, doing away with public-law religious corporations, this did not apply to the Metz diocese then being within Germany.

The concordat further provides for the clergy being paid by the government and Catholic pupils in public schools can receive religious instruction according to diocesan guide lines.