The diocese was restored (with a different boundary) by Pope Leo XIII on 4 March 1878; it is now based in the city of Dundee.
Dunkeld Abbey was an offshoot of Iona, perhaps founded in the early 9th century, in the reign of Caustantín mac Fergusa, King of the Picts.
While it is true that medieval churchmen took an active part in secular affairs (some fought in battles), that didn't make them in any sense "lay."
Medieval monarchs enjoyed considerable authority over the church, and doubtless, these positions were awarded to royal favorites.
Where known, the date of installation and ordination as bishop are listed in the notes together with the post held prior to appointment.)