He was at the University of Paris, and a roll of the year 1349 has one "Master William de Wardlaw" in the English Nation.
On 23 December 1383, during the Western Schism in which the Kingdom of Scotland sided with the Avignon Papacy, Avignon Pope Clement VII made Walter a cardinal priest (without title, that is, title to any church in Rome to which he would have been theoretically attached).
In the following year, on 24 November 1384, the same pope granted Wardlaw with the powers of a legate in Scotland and Ireland.
However, after a papal grant he retained administration of the diocese and continued to use his Glaswegian episcopal seal.
For instance, in June, 1369, Walter was ambassador in England, and in 1384, he was one of the plenipotentiaries involved in negotiating the truce of 1384.