In the early 7th century, a church was built at this site, reportedly by Saint Feichin. A later building was destroyed by fire in 1114. Within the next twenty years or so, Turlough Mor O’Connor, the High King of Ireland, refounded the abbey.[1] Raiders from Munster destroyed the buildings in 1137 but they were rebuilt by King Turlough.[2] The Abbey was refounded as an Augustinian settlement in 1138. It was one of the earliest Augustinian settlements south of Armagh, which was founded in 1126.[3]

In 1198, his son, Ruaidrí Ua Conchobair (Rory O'Connor), Ireland's last High King, constructed new buildings and also lived the last 15 years of his life at the abbey.[4] He died here and was reportedly briefly buried in the abbey before being exhumed and re-interred at Clonmacnoise.[1]

Cong Abbey was also closely associated with the O'Duffy family from at least 1097 to 1501.[2] The Annals of the Four Masters record that in 1150, Muireadhach Ua Dubhthaigh, Archbishop of Connacht, died at Cong aged 75. [5] His name is inscribed upon the processional Cross of Cong.[6]

The Norman knight William de Burgh attacked Cong in 1203, and again the abbey was rebuilt.[citation needed]

In the 1307 the abbey was reconstructed and dedicated to St Mary.[3] Cong Abbey was suppressed sometime after 1542 and later fell into ruins.[2]

The last (nominal) abbot was Father Patrick Prendergast, parish priest of Cong from 1795 until his death in 1829. He was the preserver of the Cross of Cong. After his death, the cross was bought by James MacCullagh for the Royal Irish Academy.[2]

The first restoration of the abbey was started by Benjamin Guinness in 1855, soon after he had bought nearby Ashford Castle in 1852.[1]