The MacMahon family[1] originated in Ireland and established itself in France, where it gained prominence.[2] John MacMahon, an Irish doctor born in Limerick, became naturalised in France in 1749 and married Charlotte Le Belin, Dame d'Éguilly, on 13 April 1750. That same year, King Louis XV of France created him Marquis d'Éguilly.[3] His son, the second Marquis, served in the American War of Independence, including on the frigate Aigle which the British captured on 15 September 1782.[4]
A grandson of the first Marquis, Patrice de MacMahon, served with distinction as a general in the Crimean War of 1853–56 and later in the Austro-Sardinian War of 1859, winning the Battle of Magenta on 4 June 1859. The following day Emperor Napoleon III created him Duc de Magenta. Later he became President of the French Republic, serving from 1873 to 1879.
Genealogy: https://www.angelfire.com/realm/gotha/gotha/magenta.html
Further lineage in French: https://fr.wikipedia.org/wiki/Famille_de_Mac_Mahon