A mysterious figure, he emerges in 1571 as the successor to James Beaton II as Archbishop of Glasgow. He was described by Robert Keith as "a kind of titular bishop", propped up by the establishment for nominal purposes during a period of disorder. Porterfield probably held on to the archbishopric into 1572, but he disappeared from the records thereafter.
In late 1573 James Boyd became new Archbishop of Glasgow.
Porterfield is possibly the same as the John Porterfield, minister of Ayr, who died in 1604.