The Gaelic name of the town, An Leargaidh, simply means "the slopes," and the slopes have been inhabited for a very long time. The Haylie Chambered Tomb in Douglas Park dates to around 3000 BC, a Neolithic burial place once covered by a stone cairn called Margaret's Law. Then came the Battle of Largs in 1263. A Norwegian fleet under King Haakon IV had been raiding the Scottish coast, with the armies of King Magnus Olafsson of Mann and the Isles aboard. A storm beached some of his ships; a Scottish force under Alexander III attacked the salvage party. Both sides claimed victory in their own chronicles and sagas. The only independent source fails to mention the battle at all. What is certain is what came after: Haakon, fifty-nine years old, died soon afterward at the Bishop's Palace on Orkney. In 1266 his son Magnus VI agreed the Treaty of Perth and sold the Hebrides to Scotland. The Largs Viking Festival has been held each year since 1980 to mark it all, ending with a battle reenactment, the burning of a longship, and fireworks.

The pier was built in 1834, the railway arrived in 1895, and large hotels followed. Largs transformed from a village clustered around its kirk into one of the great Victorian seaside resorts of western Scotland. William Thomson, Lord Kelvin, the physicist who gave his name to the temperature scale, lived at Netherhall here and died in the house in 1907. King Haakon VII of Norway, in exile during the German occupation of his country, visited in 1944 and became the town's first honorary citizen, an elegant gesture from a town that had once fought his ancestor on the shoreline. Nardinis ice cream parlour, on the Esplanade, has been a Largs institution since the family arrived from Italy; it reopened in late 2008 after restoration overseen by Historic Scotland. St Columba's Parish Church opposite, built in 1892, holds notable stained glass and a Willis organ. The Reverend William Smith died of plague in 1647 while ministering to his parishioners and asked to be buried in Brisbane Glen, prophesying that if the two rowan trees at either end of his grave were prevented from touching, the plague would never return. The grave has been carefully tended ever since.

Sir Thomas Brisbane, sixth Governor of New South Wales, was born at Brisbane House just up the river from Largs. His name now belongs to a major Australian city. Lord Louis Mountbatten ran his D-Day planning conference here in 1943. Inverclyde Sports Centre, opened by Queen Elizabeth II and Prince Philip in 1958, became famous in the 2000s for training a generation of football managers including Jose Mourinho, Fabio Capello, Andre Villas-Boas, Giovanni Trapattoni, Marcelo Lippi, and Carlos Queiroz. The roster reads like a Champions League dynasty roll call. They came to Scotland to take their coaching badges, and the centre quietly turned out the brains of European football. Sam Torrance, the Ryder Cup-winning golfer, was born in Largs, as was the actress Daniela Nardini. Benny Gallagher of Gallagher and Lyle is a hometown export who still runs songwriting masterclasses at the Vikingar centre to encourage local musicians.

Skelmorlie Aisle, built by Sir Robert Montgomerie in 1636 as a family mausoleum, is all that remains of the medieval kirk of Largs and is now in the care of Historic Environment Scotland. The Pencil monument south of the town centre commemorates the 1263 battle. The Largs war memorial of 1920 was designed by Sir Robert Lorimer, one of Scotland's leading early-20th-century architects. Largs Thistle Football Club, the Theesel, formed in 1889 and play in gold and black at Barrfields Park; they won the Scottish Junior Cup in 1994. Largs Live brings live music to the pubs and restaurants each year on the last weekend of June. The Kelburn Garden Party draws thousands to the painted castle just south of town. The Caledonian MacBrayne ferry runs across to Great Cumbrae every half hour, and in summer the Waverley paddle steamer still calls at the pier. The slopes never quite stop receiving guests.