[2] Alongside his older brother, Connor Maguire, he was a prime mover in the conspiracy which led to the outbreak of rebellion in Ireland on 23 October 1641.
His attempt to murder Sir William Cole immediately prior to the rising failed, but the landowner Arthur Champion was killed in one of the first actions of the rebellion.
[3] In November 1641 he joined Felim O'Neill of Kinard at Newry to issue a proclamation in which the rebels claimed they were acting in defence of King Charles and Catholicism.
[5] In early 1642, he was expelled from the Irish Parliament and in the summer of the same year he was made a colonel in Owen Roe O'Neill's army in Ulster.
[1] In 1648, Maguire joined O'Neill in opposing the truce between the Confederates and Royalists; he played a prominent role in the skirmishes and evasive manoeuvrings that occurred between the two sides in central Ireland.