He was educated by Cardinal Henry, Duke of York, at the Scots College, Rome, and was afterwards a successful advocate, becoming a Doctor of Laws in 1770.

By his tact Erskine established excellent relations with the Court of St. James and the ministry, diminished the dissensions among Catholics, and avoided stirring up any anti-Catholic demonstration against himself.

During his stay in London the pope named him a full auditor, and in 1795 gave him additional powers as envoy extraordinary.

He left London in 1801 and returned to Rome,[1] where in 1803, he was installed as a Cardinal Deacon, it being revealed that he had been elevated to this office in pectore in the Consistory of February 1801.

As a member of the Sacred Congregation of Propaganda Fide, he was still useful to English Catholics, and was made Cardinal Protector of Scotland.