St Fillan was born in Ireland, the son of Feriach and St. Kentigerna. Early in the 8th C., Fillan arrived in Scotland with his uncle (later St. Comgan), mother and brothers. They settled at Loch Duich, just east of the Isle of Skye. Fillan later moved south to make his home in Strath Fillan, at the head of Glen Dochart, where he built a church. Legend has it that, during the construction, a wolf killed an ox which was being used to carry materials. Fillan is said to have convinced the wolf of the error of its ways and it took the place of the dead ox. Next to the church, near Auchentyre in Strath Fillan, was the Holy Pool, which is said to have been blessed by the Saint, and consequently developed healing powers, proving particularly curative for the mentally ill who were attracted in large numbers over succeeding centuries. St. Fillan is closely associated with Killin, where he is said to have built a mill and set up a market. His healing stones are now kept in St. Fillan's Mill in the village.
Fillan travelled around Scotland; he visited Islay, moved to Luncarty and then Struan (Perthshire). He later visited Forgan (near Pickletillem, Fife), proceeding to St. Andrew's Monastery, before spending time as a hermit in St Fillan's cave at Pittenweem. It is also likely that he travelled to Wigtownshire, because the villages of New Luce and Sorbie both had churches dedicated to St. Fillan.
He died at an old age and was buried in Strathfillan. Much later, his relics were taken to Bannockburn, where they are said to have helped Robert the Bruce win victory. Bruce later founded a Priory in Strathfillan - 2 miles (3 km) SE of Tyndrum - in Fillan's honour. Other relics, including Fillan's staff and bell, were originally kept at the church in Strath Fillan. These items were both removed from Scotland, but returned in the late 19th C., when they were deposited in what is now the Museum of Scotland.