Burgh, William Liath de (d. 1324), deputy justiciar of Ireland, was the son of William de Burgh (d. 1270), younger brother of Walter de Burgh (qv), 1st earl of Ulster, and was probably brought up in Connacht where he spent much of his life fighting for the second earl. He came to prominence in the 1290s owing to his close relationship with his cousin, Richard de Burgh (qv), 2nd earl of Ulster. He is first heard of as the defeated party in a skirmish with Mac Coughlan in 1290. On 11 December 1294 he was captured, along with Richard, by John fitz Thomas FitzGerald (qv) (d. 1316), and was held in Lea castle till probably March of the following year, when he was released. He served with Áed O'Connor (qv) against the Clann Muirchertaigh in 1296 as the Geraldine–de Burgh feud continued. The same year he founded the Franciscan abbey in Galway. Although he received a summons for the Scottish campaign in 1301 he remained in Ireland, but in July 1303 was part of the paid retinue led by Richard de Burgh to Scotland; he returned home on 27 June 1304. For this service he was rewarded with the custody of the Geraldine lands around Loch Manin.
On 1 October 1308 he was appointed deputy justiciar during the lieutenancy of Piers Gaveston (qv). In December he led an army against the Irish rebels of Leinster and in January 1309 he held assizes at Cashel. He relinquished office on 15 May and turned his attention to the outbreak of strife between the O'Connor factions in Connacht, which was threatening de Burgh power in the province. He actively opposed Áed Bréifnech O'Connor (qv), expelled his brother Ruaidrí O'Connor (qv) (d. 1316), and raided Sligo and Leitrim. The following year, after the fall of his castle near Boyle, he bribed the captain of Áed's gallowglass bodyguard to kill his master. William openly defied the legislation enacted at Kilkenny that year and forcibly billeted his mercenary troops on the land. According to the annalists, ‘he aimed at the seizing of the sovereignty of Connacht for himself’, though the dynastic vacancy of the O'Connor was short-lived.
Between 1311 and 1315 William was involved in the conflict between Richard de Burgh and Richard de Clare (qv), who supported rival O'Brien factions in Thomond. During the summer of 1311 he invaded de Clare's lands with Donnchad O'Brien (qv), but on 20 May at a battle near Bunratty his forces were defeated and he was captured; his ally fled but was afterwards killed. Richard de Burgh negotiated his release in July and he returned to raid Thomond the following autumn, defeating Diarmait O'Brien. Despite truces between the two sides, fighting continued sporadically and William led occasional raids from his stronghold of south Galway. The conflict effectively ended in 1315 when the Scots invaded Ireland. In July of that year William joined the earl of Ulster in Connacht to raise an army to oppose Edward Bruce (qv). At the battle of Connor on 10 September the de Burgh army was completely defeated and William was taken prisoner. His release was secured by Richard who commandeered a fleet marked for the relief of his own castle of Carrickfergus in July 1316, surrendered it to the Scots, and handed over William's son Edmund (qv) as a hostage for his father's good behaviour. By the end of July William was back in Connacht. He raised a motley army of Anglo-Norman colonists and Irish chieftains who had remained loyal to the earl and marched against Fedlimid O'Connor (qv), who had taken advantage of the chaos to lay waste to the province. On 10 August, after a particularly bloody battle at Athenry, William was victorious.
Thereafter it appears that he remained in Connacht consolidating de Burgh power. In July 1322 and April 1323 he accompanied Richard to the English court and in November he was high in the list of magnates ordered to give counsel and aid to the new justiciar, John Darcy (qv). He died the following year and was buried at the Dominican abbey at Athenry. He had married Finola, daughter of Brian Ruad O'Brien (qv), one of his cousin's early allies, with whom he had three sons and one daughter.
In William de Burgh, the earl of Ulster had a very capable and loyal lieutenant. From 1305 onwards he was lord of Connacht in all but name, allowing Richard to concentrate on the rest of his sprawling domains. The fact that Connacht did not collapse during the Bruce invasion was primarily due to William's ability and his strong ties to many of the leading Irish families of the province. Ironically his success in building a local power base there was to lead to conflict between his heirs and the next earl of Ulster.