Echmarcach (d. 1064/5), son of Ragnall and king of Dublin and the Isles, belonged to the Hiberno-Norse ruling dynasty of Waterford. As his father Ragnall had been slain (1035) by King Sitriuc Silkbeard (qv) of Dublin, Echmarcach forced Sitriuc's abdication in 1036 and succeeded to the kingship of Dublin, the authority of which at that time extended over Man and the Isles. It is difficult to avoid suspicion of complicity on Echmarcach's part when, within that same year, Gofraid son of Sitriuc was slain in Wales by one Glún Iarainn.
In 1038 Echmarcach was displaced from the kingship of Dublin by Imar son of Harald, who was probably a nephew of Sitriuc. He regained control of the town eight years later, but was deposed (1052) by the powerful Leinster king Diarmait (qv) son of Donnchad Máel na mBó (qv). Having fled to the Isle of Man, he retained a kingship of the Isles for a further nine years. In 1061 Man was invaded by the Leinstermen under Murchad (qv) son of Diarmait. Echmarcach was defeated and took flight, leaving control of Man to Murchad. It would appear that he retained a rump kingdom based on the Rhinns of Galloway, which would explain his being styled rex Innarenn (king of the Rhinns) by Marianus Scottus (Máel-Brigte) (qv).
Finally, in 1064, Echmarcach decided to abdicate his kingship and travelled to Rome on pilgrimage in the company of Donnchad (qv) son of Brian Bórama (qv). Echmarcach died later that year, or early in 1065. His nephew, Gofraid son of Amlaíb (Óláfr) son of Ragnall, reigned as king of Man and the Isles after 1070.