Essential advice from Póilín on Papists, Royalists and parties
Until the late 19th century, any Joe Soap could be made a cardinal or pope. Leo XIII got a bit more stringent, and said that Joe Soap would at least have to be ordained Fr Joe Soap once he had been so appointed. Then John XXIII said that he'd have to be made a bishop as well – but this after he had been nominated as cardinal or pope.