The name "Leuchars" is of Celtic origin, related to Llwchur in Wales, meaning "a stream flowing through marshy ground". The original chapel, dedicated to St Bunan, or St Bunoc (the village of Leuchars has a street named St Bunyan's Place) is thought to date back to around the year 900 and was served by Culdee priests. Later, Roman Catholic clergy officiated until the Reformation in the 16th century. A stone from the chapel graveyard, believed to be of Pictish origin, was discovered when Leuchars Castle was demolished in 1948. It can now be seen in the church.
The present building is an amalgam of building projects, alterations and extensions spanning a period of more than 800 years. Recent research suggests that the oldest (Norman) part of the church - the apse - dates back to the 1140s or 1150s, and it has been described as "possibly the finest Romanesque church in Scotland" (Fife, Perthshire and Angus by Bruce Walker and Graham Ritchie).
It can be verified from ancient records that the "Ecclesia de Lochres" was granted to the Priory of St Andrews by Ness, Lord of Lochore (Leuchars) between 1183 and 1187. Ness was the last chief of his line and his estates passed to his daughter, Arabella. She married Robert de Quinci, a member of a Norman family settled in Northamptonshire. Robert was honoured by being chosen to escort King William the Lion to Scotland in 1175. Prior to 1175, Robert was married and had settled in Leuchars. It is likely that his mother Matilda started the church building.
The de Quinci family, wealthy and well-connected, was to have a profound influence on the community at Leuchars. Robert built Leuchars Castle, on the motte to the north of the church. As local landowner, it was his responsibility to build a church. Perhaps he would have done more, had he not opted to fight in the Crusades - he was killed in Palestine in 1192.
Robert's son Saieur, consolidated the family's fortunes and added considerably to the de Quinci estates: Tranent in East Lothian, valuable for its coal and Forfar Castle, for example, came into his possession. He was also involved in trade and had ships sailing up from Norfolk to Guardbridge.
Through a subsequent marriage to a daughter of the Earl of Leicester, Robert also acquired estates in England. Subsequently his considerable abilities came to the attention of King John, who made him Earl of Winchester and entrusted him with a number of diplomatic missions at home and overseas. He was a signatory to the Magna Carta.
Following in his father's footsteps, he continued the building of St Athernase but did not survive to see its completion in 1220. Having gathered a large force of his retainers from Leuchars and elsewhere, he embarked on the Crusade to the Holy Land, and died at Dalmietta in 1219.
In the time of Saieur's son, Roger, on 4th September 1244, by Papal decree, the church was dedicated to St Athernase by the Bishop of St Andrews, David de Bernham. As the Celtic or Culdee Church of Scotland had developed from Ninian and Columbia, it had not followed the forms of the Roman Church and there was no tradition of dedicating churches to saints. Over a ten-year period, the Bishop of St Andrews dedicated approximately 140 out of the 300 churches in his diocese.
Virtually nothing is known of Athernase. If it is true that he had a tendency to stutter, then this may explain the reason for his absence from the limelight. He is thought to have spent much of his life in mid Fife, a contemporary of St Columbia in the 6th century. A variant of his name is "Ethernesc", who is recorded as son of Angus, brother of Ternan (the name "Ternan" appears in two churches in the town of Banchory in Aberdeenshire).