[1] Part of the Argyll and Bute council area, they lie in Firth of Lorne west of Lunga and northwest of Scarba and have been uninhabited since the 19th century.

[2][a] The islands are known for their early Christian connections to Brendan the Navigator and Columba and for their bedrock containing rare formations in relation to the global Sturtian glaciation.

Garbh Eileach is the largest island in the group and extends to 142 ha (351 acres) and reaches a maximum elevation of 110 m (361 ft) above sea level.

[8] The geology of the Garvellachs consists entirely of rocks of the Neoproterozoic Dalradian Supergroup apart from several basaltic dykes of Palaeogene age, associated with the nearby Mull Igneous Centre.

The sequence contains 48 diamictite beds, while 35–40 % of the formation is formed of sandstone of non-glacial origin, deposited in a deltaic to shallow marine sedimentary environment, interbedded with minor amounts of siltstones and dolomites.

Dating of the Port Askaig Tillites has been attempted using a wide variety of techniques, but these have produced contradictory results, with evidence found that supports both of the options.

Samples from the sandstones (those from the Garbh Eileach Formation and three lower members of the Port Askaig Tillite were all taken from the Garvellachs) have been analysed using detrital zircon geochronology and the results provide the strongest support for the sequence being Sturtian, with "youngest single grains" throughout being consistent with the likely depositional ages.

There is a ruined castle on the top of Dùn Chonnuill that may have been built by the Macleans of Duart in the early fifteenth century after the island was received by them as a gift from King Robert III.

[3][17] Brendan is said to have been buried on A’ Chùli[9] although no trace of his chapel there remains[18] and a similar fate appears to have befallen two unroofed buildings, thought to be shielings, recorded in 1881 by the Ordnance Survey.

[4] The outcrops of limestone on Eileach an Naoimh give rise to fertile soils and the slope of the land makes for "verdant" south-facing hillsides.