Bourke, Theobald (c.1615?–1653), 3rd Viscount Mayo , soldier and politician, was son and heir of Miles Bourke (qv), 2nd Viscount Mayo, and Honora, daughter of Sir John Bourke of Derrymaclaghtny, Co. Galway. Educated in the protestant faith at Oxford, under the direction of Archbishop Laud, Bourke returned to Ireland to pursue a promising political career. Created a baronet in 1638, he married Elizabeth, daughter of Thomas Talbot of Bashall, Yorkshire, a union that produced four children: Miles, Theobald (his successor as viscount), Margaret, and Maud. After Elizabeth's death he married Eleanor, daughter of Sir Luke Fitzgerald of Tecroghan, Co. Meath. Bourke represented Co. Mayo in the 1640–41 parliament, which his father also attended as a member of the house of lords. Both remained loyal to the Dublin administration in the early months of the 1641 uprising, working closely with their kinsman, Ulick Burke (qv), 5th earl of Clanricarde.
On 13 February 1642 a convoy of protestant refugees, escorted by Theobald, was massacred at Shrule on the Mayo–Galway border. Bourke, although technically in command, proved powerless to prevent the killings. Both father and son, fearful of government reprisals, joined forces with the rebels in Connacht, openly converting to catholicism at the same time. Bourke attended a provincial assembly at Ballinrobe, Co. Mayo, on 15 September 1642, and the following month represented Mayo at the first confederate general assembly in Kilkenny. He concentrated his energies primarily on military affairs in Connacht, capturing Sligo in 1645, and campaigning in Mayo the following two years. Bourke was a political moderate, and the royalist earl of Clanricarde described him as ‘a person very necessary to curb turbulent dispositions in the county of Mayo’ (Lowe, Clanricarde letter-book, 281). The final confederate assembly in October 1648 appointed Bourke as one of the commissioners to negotiate the peace treaty with Ormond (qv), signed on 17 January 1649. He succeeded his father as viscount later that year, and throughout the Cromwellian war operated martial law in Mayo. Captured by the forces of the English parliament in 1652, he was tried and found guilty for the murders at Shrule. A witness to his execution (15 January 1653) reported how ‘the soldiers appointed to execute him missed three times, but at last a corporal blind of an eye, hit him’ (quoted in Galway Arch. Soc. Jn., xliv (1992), 110, n. 69). He was buried in Galway, and his lands declared forfeit. His son Theobald recovered the family estates after the restoration of Charles II.