Obligated to flee the monastery with the other monks due to the Napoleonic invasions, he became an itinerant professor in Karlsruhe, Paris, London, Glasgow, and Dublin.

Count Metternich, the Austrian ambassador, and his secretaries followed the whole course of lectures, and spoke in highly laudatory terms of the system, which, though novel in its applications, was founded on the topical memory of the ancients, as described by Cicero and Quinctilian.

Feinaigle was exposed to much criticism and sarcasm in the press, and was ridiculed on the stage by Dieulafoy in a farce called 'Les filles de mémoire, ou le Mnémoniste.'

Peter Baines, afterwards bishop of Siga, introduced his system of mnemonics and also his general plan of education into the Benedictine college of Ampleforth, Yorkshire, and a society of gentlemen founded a school in Aldborough House, near Mountjoy Square, Dublin, which was placed under Feinaigle's personal superintendence and conducted on his principles.

Other treatises on the system were: Gregor von Feinaigle is credited by some[3][4] as being the inspiration for the word "finagle" meaning "To cheat or swindle; to use crafty, deceitful methods."