Gilla Asalta appears to be solely known via an obituary in the Annals of Tigernach under the year 1172, which states:
Gilla Asalta, senchaidh Ruaidhrí Uí Concobair ríg Erenn, ard-shái na n-Gaidhel ina aimsir, mortuus est/Gilla Asalta, chief historian of Ruaidrí Ua Conchobair king of Ireland, the chief sage of the Gaels in his time, died.