The diocese was erected in the 4th century and presently covers the same territory as Belgium's Liège Province, but it was historically much larger.
The original diocese was the church equivalent of the Civitas Tungrorum, the capital of which was Tongeren, northwest of Liège, and its borders were probably approximately the same.
In late antiquity, the centre of administration and religion in the area moved first to Maastricht, and then to Liège.
Thus the diocese of Tongeren extended from France, in the neighbourhood of Chimay, to Stavelot, Aachen, Gladbach, and Venlo, and from the banks of the Semois as far as Ekeren, near Antwerp, to the middle of the Isle of Tholen and beyond Moerdijk, so that it included both Romance and Germanic populations.
On his grave Hubert built a chapel (St. Lambert's Cathedral) which became the nucleus of the city, and near which the permanent residence of the bishops was established.
To Stephen, a writer and composer, the Catholic Church is indebted for the feast and the Office of the Blessed Trinity.
The original dioceses of the region underwent some adaptations under Habsburg influence in 1559, and then survived further until suppression under the Revolution, and confirmed in 1801 by a Concordat co-signed by Napoléon Bonaparte and Pope Pius VII.
The present Diocese of Liège, suffragan to the Archdiocese of Mechlin–Brussels, consists of 525 parishes with 543 priests and has a population of 1,023,506 (as of 2003[update]), the majority (Walloons) speaking French; the minority speaking German in the Eupen-Malmedy area, part of Germany until the fallout after World War I.