In May 1577, Sir Nicholas was appointed chief commissioner of Ulster, with Henry as his assistant. Bagenal was himself knighted in 1578. He was involved in some military disasters, such as a defeat at
Glenmalure on 25 August 1580 when
Lord Grey led the troops (with Bagenal one of the commanders of the rear) into battle with
Fiach McHugh O'Byrne and
Viscount Baltinglass in the
Wicklow mountain passes. In 1584, Bagenal was colonel of the garrison at
Carrickfergus when 1,300 of
Sorley Boy MacDonnell's Scots landed on
Rathlin Island. Bagenal attacked but was ambushed at
Glenarm and had to retreat. In May 1586, Bagenal was sent by his father to the court to report. He sought measures to weaken
Hugh O'Neill, Earl of Tyrone, an enhancement of the role of the marshal, and a presidency in Ulster with a shire hall and jail to dispense royal justice. Whilst on his visit, he wrote to
Edward Manners, 3rd Earl of Rutland (a relative of his wife) on 16 September 1586 to ask whether he had a parliamentary borough to spare; he was elected MP for both
Grantham and
Anglesey and chose the latter. He returned to Ireland in September 1587 to deputize for his father. He succeeded his father as marshal of the army in Ireland and chief commissioner for Ulster in October 1590, and was sworn of the
Privy Council. His proposals for action were not accepted, as a decision had been taken to adopt a conciliatory attempt to O'Neill. To Bagenal's contempt, O'Neill asked for the hand of Bagenal's sister
Mabel in marriage; he refused, but they eloped anyway. ==Family==