Burke (de Burgh), Walter (d. 1440), and Edmund (‘na Féasóige’) (d. 1458), 3rd and 4th lords of Lower Connacht (Mayo), were sons of Thomas Burke (qv), 2nd lord. Although Walter was recognised as the rightful successor to his father, throughout their lives Edmund seems to have been the more active of the two. Walter recognised Uilleag ‘an Fhiona’ Burke (qv), 3rd lord of Clanricard, as the senior MacWilliam. In 1402 he joined Uilleag an Fhiona and the earl of Ormond (qv) on a campaign against the earl of Desmond. In 1411 Edmund na Féasóige asserted his brother's supremacy over the O'Haras and in 1417 he captured Mac Feorais (de Bermingham) and imprisoned him. In 1419 he allied with the O'Kellys and launched a massive raid into Clanricard, but was beaten off with heavy casualties. This defeat underlined the supremacy of the Clanricard Burkes, and the Burkes of Mayo remained quiet for the rest of Walter Burke's lifetime.
When Walter died of the plague in 1440, he was succeeded not by his son, Theobald, but by Edmund na Féasóige, indicating that the MacWilliam Burkes of Mayo were moving steadily away from primogeniture to a more Gaelic form of inheritance. Edmund na Féasóige proved to be a very active leader and in 1443 he invaded Clanricard, forcing Uilleag Burke (qv), 5th lord of Clanricard, to acknowledge his supremacy. This state of affairs probably lasted for less than a decade, as Uilleag Fionn defeated the sons of Walter Burke (1449) after they raided into Galway. Edmund na Féasóige also attempted to forge alliances in Ulster. In 1452 the earl of Ormond forced Énrí O'Néill (qv), lord of Tír Eóghan, to put aside the daughter of MacWilliam Burke, the widow of Neachtan Ó Domhnaill (O'Donnell) (qv), lord of Tír Conaill. Clearly, Edmund na Féasóige was attempting to make firm alliances to bolster his position in Connacht. When he died in 1458, the lordship of Lower Connacht passed to his brother Tomás Óg. Poems in Irish addressed to Walter and Edmund na Féasóige are in Aithdioghlium Dána (ed. by L. McKenna, Irish Texts Society, 1940).