E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Irrespective of all external considerations of right or wrong; absolutely; by the very deed itself. It sometimes means the act itself carries the consequences (as excommunication without sentence of excommunication being directly pronounced).
Whatever the captain does is right ipso facto [i.e. because it is done by the captain], and any opposition to it is wrong, on board ship.R. H. Dana.
By burning the Popes bull, Luther ipso facto [by the very deed itself] denied the Popes supremacy. Heresy carries excommunication ipso facto.