In August 1594, an English supply column under Sir Henry Duke was marching from Cavan toward besieged Enniskillen, loaded with provisions for the garrison there. Hugh Maguire of Fermanagh, working with reinforcements from Hugh O'Donnell, set an ambush at a narrow ford a few miles short of Enniskillen. The Annals of the Four Masters describe what happened in considerable detail: 'a fierce and vehement conflict, and a spirited and hard-contested battle.' Bingham's force was routed. A countless number of nobles and commoners fell. Most importantly for what came next, the defeated army left behind their horses and pack animals, all loaded with provisions, including a huge quantity of biscuits and small cakes. The ford was renamed Bel-atha-na-mBriosgadh, the Ford of the Biscuits, and the few survivors fled back through Largan, the territory of the Clann-Coffey Magauran. Largan was the original name of Blacklion.

When King James I parcelled out confiscated Gaelic lands during the Plantation of Ulster, the territory of Largay went to an Englishman named Nicholas Pynner. The patent, dated 14 December in the 13th year of James I, granted Pynner 'the Precinct of Toom, containing 4 polls, called Gortnesillagh, Mullaghgarrowe, Rossan and Ture or Toore.' Total rent: one pound, twelve shillings. The Coffey McGoverns, a sub-sept of the McGovern clan who had held these lands from the 9th century, lost everything. By the Commonwealth Survey of 1652, the lands were owned by Thomas Worship and tenanted by Lan Lawther. In 1625, the McGoverns and Maguires planned an uprising against the English Crown, allegedly in anticipation of a Spanish landing. The Fermanagh Assize Judges arrested the ringleaders, tried them by a jury of English freeholders, and found them all guilty.

The village name changed in the eighteenth century, in honour of a famous coaching inn called the Black Lion. Wilson's Post-Chaise Companion of 1786 records the location: 'About a quarter of a mile to the R. of Largay, or the Black Lion inn, is Belcoo Bridge.' One traveller who took advantage of local hospitality in this area was John Wesley, founder of Methodism, who visited in the 1770s during one of his many tours of Ireland. Caught in bad weather, he ended up at a remote inn called Carrick-a-Beg, where, as he wrote, 'we made a hearty supper, called in as many as pleased of the family to prayers, and, though we had no fastening either for our door or our windows, slept in peace.' Whether this was the Black Lion or another nearby inn remains uncertain. Blacklion was the first place in County Cavan to be affected by the potato blight in the autumn of 1845, and deaths in the subsequent Great Famine were high.

Three kilometres south of Blacklion lies the Cavan Burren Park, a limestone landscape full of Neolithic remains: dolmens, ringed forts, cairns, the Calf House or Druid's Altar portal tomb, and the Giant's Leap wedge tomb. The area was planted with conifers in the 1950s, then partially reclaimed in recent decades and signposted to provide access to the structures and the geological features beneath the trees. The Cavan Way, a 25-kilometre marked walking trail, runs from Dowra through this landscape to Blacklion, where it links up with the Ulster Way. From here you can walk to Shannon Pot, the traditional source of the River Shannon, or up the slopes of Cuilcagh Mountain via the famous boardwalk. Cladagh Glen Nature Reserve and the Hanging Rock lie just to the north across the border, all part of the cross-border Cuilcagh Lakelands Geopark, the world's first transnational UNESCO geopark.

Two cultural names define modern Blacklion. The first is the eighteenth-century Gaelic poet Cathal Bui Mac Giolla Ghunna, born in Barran townland three miles from Blacklion. His most famous poem, An Bonnan Bui, 'The Yellow Bittern,' laments the death of a bird that perished from thirst, and is one of the great lyric poems in the Irish language. There is a monument to him on the shore of Upper Lough MacNean, two kilometres from Blacklion on the Sligo road. The second name is Neven Maguire, born in Blacklion in 1974, who runs MacNean House and Restaurant out of his family's village. Maguire is one of Ireland's best-known television chefs and has made Blacklion a destination for food tourism in a way few small border villages have managed. The local GAA club, Shannon Gaels, takes its name from Shannon Pot just south of the village, and is the most westerly and northerly Gaelic Athletic Association club in County Cavan. The village that began as a battlefield over biscuits is now a place people travel hours to eat in.