MacGeoghegan, Arthur (c.1600–33), Dominican priest, was almost certainly a Westmeath kinsman of his fellow Dominican Ross MacGeoghegan (qv). His original name was most probably Art Mac Eochagáin. He entered the Dominican order as a filius of Mullingar, though the date is unknown. He started his studies in Spain in 1622 and was listed as a clerical student there in 1627, as were Irishmen of his name, Patrick and Dominic MacGeoghegan. Described as an alumnus of the nascent Irish Dominican college in Lisbon, he may have been ordained priest there. Certainly by 1631 he was a member of the Dominican hospice located in the Calçado do Combro area of the city, before it moved to a site close to the Italian church of Our Lady of Loreto. He was chaplain to the Spanish navy and port chaplain at Lisbon, his duties including the censorship of imported books and inspection of suspect English and Dutch ships, Spain being then at war with the Calvinist Netherlands. It was partly because of his proficiency in English and several other languages that the Spanish viceroy in Portugal had employed him in this work. In December 1631, while pursuing his duties, he detained an Englishman, a Captain Bust, whose ship had been confiscated on suspicion that it was Dutch. He engaged Bust in theological and apologetical arguments especially concerning free will, a disputation that Bust did not forget.
In the spring of 1633 MacGeoghegan set out for Ireland via London to select students for the new Lisbon college and also to transact some business for the viceroy of Portugal. While in London, he encountered Bust again, who had him imprisoned; Bust charged that MacGeoghegan had said at Lisbon that if he ever returned to England, he would kill the king as a heretic. Under questioning, MacGeoghegan admitted some slight grounds for the charge, but insisted that his words had been misconstrued. He explained that what he had hypothetically said (‘it would be no sin to kill the king’) in his apologetical argument with Bust was that, without free will, fanaticism would find its excuse, even if a man were to assassinate the king of England. Few believed his account, and all defence proved useless. King Charles I, hearing the case, privately expressed the hope that the Dominican would be acquitted, but refused to voice his view in the face of the known hostility of the judiciary and current anti-catholic public opinion. The king's minister Sir Francis Windebank and Queen Henrietta Maria also tried to save MacGeoghegan from false conviction as a traitor, but he was convicted for ‘speaking treasonable words’, before the king's bench on 25 November. On 27 November 1633 Arthur MacGeoghegan was executed at Tyburn ‘in odium fidei’. His body underwent the barbarous mutilation prescribed for treason but, contrary to custom, his members were not displayed upon the four gates of the city of London. He was either buried beneath the scaffold or perhaps more likely carried off by influential sympathisers to be interred respectfully elsewhere.
His execution gratified that portion of the London populace that believed catholics to be regicides. According to another testimony, the death of Arthur MacGeoghegan did more good than injury to the catholic cause, as almost everybody judged that he died innocent of the crime of which he had been accused. The original minutes of his arraignment on the false charge of high treason are preserved among the muniments of the duke of Westminster at Heaton House, Cheshire. The general chapter of the Dominican order held at Rome in 1644 recorded and eulogised his martyrdom in its proceedings.