If he was in army or militia there were ample reasons for him to be sent to Ireland.
There was a major European war going on as a consequence of the French Revolution 1789. Britain and her allies were at war with France from the early 1790s, after execution of King Louis until 1815, with a couple of brief armistices. The new French government was succeeded in time by Napoleon Bonaparte who made himself Emperor and had ambitions to conquer the rest of Europe and parts of overseas territories of other European powers. So it wasn't just a European war, it stretched across the globe.
Britain was at risk of French invasion. A few French troops did manage to land on the south coast of England. On another occasion Jane Austen, out for a cliff-top walk, witnessed a naval battle.
The territory most vulnerable to French invasion was Ireland, "England's back-door". Ireland had to be well fortified.
Ireland was having its' own insurrections and rebellions at this time. There was sectarian violence in some counties. (G***le Whiteboys, Defenders, Oakboys, just a few of the many local groups causing mischief.) There was a Parliament in Dublin, with very limited powers and subject to the British Parliament in Westminster. Inspired by French Revolutionary ideals, the Society of United Irishmen was founded (g**le it). One of the leaders, Wolfe Tone and some others, went to Paris to get support from the French government. A French invasion fleet was promised. Meanwhile back in Ireland the authorities were cracking down on any possible dissent. Brutal methods of coercion included pitch-cappings and half-hangings; and that was just for suspects or to make an example of someone as a warning to others. The Orange Order was also founded in the 1790s and was encouraged by the authorities as a defence against the United Irishmen movement. (The Society of United Irishmen was non-sectarian, many of the leaders were Protestant.) First attempted French invasion fleet was unsuccessful. 1798 was the year of Irish rebellions. That Spring there were United Irishmen risings in County Wicklow (just south of Dublin) and Wexford further south. There were atrocities on both sides. Defeat of the rebels was followed by executions and more repression. Late that summer the French invasion force finally landed in the western county of Mayo. Locals joined them. They took the town of Castlebar and proclaimed the Republic of Connaught. Success and the republic were short-lived. After their defeat the French army was treated honourably as POWs but it was a different story for the native Irish, being rebels.
A consequence of the 1798 rebellions was abolition of the Irish Parliament a few years later. Some Irish MPs were allegedly bribed to vote for abolition.
Robert Emmett planned a rising in Dublin in 1803 but he was arrested and hanged.
Thousands of troops were stationed in Ireland at any one time from late 18thC- late 19thC. One source suggested as many as 20,000. (My own grandmother married one of them.)
From research I've done on another branch of my family I know that all 3 regiments of the Lancashire Militia, comprising around 3000 men were stationed in Dublin 1813-1816. They were supposed to go to Ireland in the 1790s as well to see off one of the imminent French invasions but were delayed. They also made a trip to Scotland. They spent most of the war on the south coast of England, but went on occasion to N.E. England.
You did ask.
(As well as me being part- Irish this was one of my A level History topics.) Lots more information available.
Soldiers who wanted their wives to accompany them drew lots to decide. Wives were a asset to the regiment. They were laundresses (waging war on lice) and nurses.
You might find your tailor on muster rolls if they survive.
Have you tried "Overseas Births"? I don't know if the register goes back that far.
