Having completed his formal education at the local classical school in Manorhamilton, John went to work as a draper’s assistant in his father’s Cloth Hall in the town. At the age of 23 in 1867 he responded to a Papal appeal for volunteers from around the world to come and defend Rome against attacks by King Victor Emmanuel who was intent on securing the unification of all of the states in the Italian peninsula. Rome was captured by the Italians three years later. McGuinness returned home, but for many years afterwards he was referred to as ‘the man who fought for the Pope’. Following his marriage to Teresa Timoney from Garrison, John established his own drapery and millinery business in the Commercial House (now Manor Chemists) in Main Street. He also involved himself prominently in local church and political matters. He raised substantial funds for the building of the Catholic churches in Manorhamilton and Kiltyclogher, and was president of the local branches of the St. Vincent de Paul Society and the Temperance League. Being also a staunch nationalist, he took a prominent part in the Land league and National League. He was elected to the Board of Guardians of Manorhamilton Poor Law Union and later Leitrim Co. Co. and Manorhamilton District Council. He played a significant role in the provision of a public running water supply and electric lighting for the town, as well as in the acquisition of the Bee Park as a public amenity ground. When he died in February 1931 he was survived by five of his six children.