Edmund first came to attention in 1443 when he instigated the murder of Finan and Dermot MacGillapadraig, the sons of the King of the ruling Irish clan in Ossory.
In 1462, his second cousin John Butler, 6th Earl of Ormond, arrived in Ireland with the objective of opening another front against the Yorkists during the Wars of the Roses.
Enlisting Edmund MacRichard's help, he captured Waterford and along with it, the son of the Earl of Desmond.
Edmund swept down to meet him but was heavily defeated, losing 400 men and was captured at the Battle of Pilltown.
It was said that part of Edmund's ransom was paid with manuscripts from his library including the Psalter of Cashel which contained genealogies, the Calendar of Aengus and a Glossary written by Cormac mac Cuilennáin, King Bishop of Cashel, which was the first comparative dictionary written in Europe.