Walsh is the fourth most popular family name in Ireland, but the Walshs do not have a common ancestor. The name derives from the Welshmen who came to Ireland in the 12th century with the Anglo-Norman invasion. It is common all over the country, but especially in the south-east, in Waterford city and county. There, it is often pronounced "Welsh," true to its origins.

Among the famous Walshs was Maurice Walsh, the former customs officer, who wrote The Quiet Man, an Oscar-winning film whose cast included Maureen O'Hara and John Wayne. Other and earlier Walshs included Thomas FitzAnthony Walsh, who was the Governor of Leinster in the 13th century. He built the fortifications at Thomastown, Co. Kilkenny, fragments of which can still be seen today, together with the near by Grenan Castle, now in ruins. Father Michael Walsh (1828-1866) was the parish priest of Sneem, Co. Kerry, and the "Father O'Flynn" of the famous song.

The Walshs have no clan head and, although the name is so widespread, there is no clan seat.