Maxwell, an officer of dragoons, spent much of his career with the English and subsequently the Irish Royal Army; during the Williamite war in Ireland he was a member of the Jacobite party, remaining loyal to the deposed James II.

Travelling to Ireland, where the army remained under James's control, he was given the colonelcy of the Seventh Regiment of dragoons; he was stationed at Bangor in eastern Ulster at the time of the main Williamite landings in 1689.

Another faction of the Jacobite leadership, led by Patrick Sarsfield, opposed seeking a settlement; when in late 1690 they sent fellow generals Luttrell and Purcell to France to argue their case, Berwick ordered Maxwell to accompany them, with secret instructions to have them arrested on arrival.

[6] According to Berwick's memoirs, Luttrell and Purcell discovered the plan during the voyage and suggested throwing Maxwell overboard, before being dissuaded by the Bishop of Cork.

[6] During the 1691 campaign Maxwell was assigned as commander of the garrison of Athlone during its siege by the Williamite army; the efforts of his regiment of dragoons to defend the bridge over the River Shannon later became a celebrated example of bravery.