He was born at Aughnasheelan, Ballinamore, County Leitrim, the son of small farmer Francis McCartin and his wife Annie Kate Lohan. He was educated at Drumbibe National School, Aughnasheelan and St. Patrick's College, Cavan. In 1972, he married Ann Clarke; they have two sons. As a young farmer, McCartin was awarded many national prizes for progressive and efficient farming. He founded the McCartin Bros group of companies with his brother Tommy; these had interests in Structural Steel, Clothing Manufacture, Milling, Forestry, Pig Production, and Dairy/Beef Farming. They quickly became the largest employers in Leitrim.
Political career
McCartin joined Fine Gael as a teenager and became secretary of the Ballinamore District Executive at the age of seventeen. He served as county secretary of Macra na Feirme and was a member of its national executive. He was Chairman of the fundraising committee which established the first rehabilitation centre in the north-west of Ireland. He was elected to Leitrim County Council in 1967. In 1973, he was elected to Seanad Éireann as a Senator for the Agricultural Panel, and after his re-election to the Seanad in 1977 he was elected Leas-Chathaoirleach of the 14th Seanad. He was elected to the European Parliament in 1979 for the Connacht–Ulster constituency and to the Dáil at the 1981 general election representing the Sligo–Leitrim constituency. He served as secretary of the Fine Gael Parliamentary Party, Secretary of the Opposition Front bench and party Spokesperson for Agriculture. He lost his seat at the February 1982 general election but regained it at the November 1982 general election. He lost it at the subsequent 1987 general election and did not stand in any further Dáil elections. In the European Parliament, McCartin was elected Vice Chairman of the Parliament's Budgetary Control Committee. He was the first Irish person ever to hold the position of Vice President of the European People's Party. He also served on the parliament's Agriculture and Fisheries committees. He was Joint Auditor of the European People's Party, along with former TaoiseachJohn Bruton. He retired from the European Parliament in 2004, having become Ireland's longest-ever serving MEP. In 1974, he was elected Leitrim Person of the Year. In 1977, he was named as one of Ireland's "People of the Year" for "bringing hope to a depressed area." In 2004, he was presented with the Schuman Medal at a meeting of the European Christian Democrats in Budapest, Hungary, for "his outstanding contribution to peace and unity in Europe and for the promotion of the human values of mankind".