The Monarchist Party was almost always the majority party within the Imperial Parliament during the time of the Star Imperium. It always favored the rule of Imperial Sovereigns (or at least Quasi-Sovereigns), but in practice that office was vacant, and divisions of the Monarchists into Blue Monarchists, Red Monarchists, and the Moderate Party, thanks to divisions caused by the mixing of religion and politics by many advocates of Monotheism and Incarnatism often made it difficult to elect a Sovereign by a Parliament majority, in practice leading to the regencies of the Council of Twelve.

The Monarchist Party mainly disappeared with the rise of the United Planets.