Irish is an immigrant to the United States from Ireland, still possessing a thick Irish brogue. He is a dysfunctional alcoholic known to greatly exaggerate, and tell tales of which he seldom remembers the finer details. When John Marston works alongside him, he often does the work while Irish is nowhere to be found, further perpetuating his reputation as a lazy drunk and a coward.
Irish is one of the supporting characters in the first chapter of Red Dead Redemption. His help was suggested to Marston by Nigel West Dickens as the man who could get Marston heavy firepower and ammunition from a Gatling Gun. After saving Irish from two of his "friends", and rescuing his friend Shaky, while also carrying out other errands, he will "help" John take over the hideout of Bill Williamson — Fort Mercer. However, when the battle starts in Fort Mercer, he is nowhere to be found until just before the mission is finished. His excuse: "I awoke with me head in a pair of tits and it felt ill-mannered not to get reacquainted with them." In the mission "We Shall Be Together in Paradise," however, Irish provides John with a raft to Nuevo Paraíso and accompanies him, even if he cowers while they're under fire.
After arriving in Nuevo Paraíso, Irish is never seen again. In 1914, the "miscellany" section of the Blackwater Ledger states that an "Irish male, of unknown name, came to his death by the accidental discharge of a gun in a Thieves' Landing outhouse."
- During the mission "We Shall Be Together in Paradise", Irish mentions he was born into the world fighting and he will leave it fighting, to which John replies that he thinks Irish will leave it pissing his pants. Ironically, this predicts Irish's death in the future when his gun accidentally goes off in an outhouse in Thieves' Landing.
- "A Frenchman, a Welshman and an Irishman" (Boss)
- "Man is Born Unto Trouble" (Boss)
- "On Shaky's Ground" (Boss)
- "The Assault on Fort Mercer"
- "We Shall Be Together in Paradise" (Boss)
At least one news outlet criticized the portrayal of Irish as the "town drunk" who attempts to talk his way out of situations as being the "Stereotype of the drunken Paddy." 
- Main article: Irish/Quotes
- “They call me El Rato, 'The cat', on account of me stealth and cunning.”
- — Irish
- “What's the word for 'cunt' in Spanish?”
- — Irish
- “Ain't you got some peckers to be suckin'?”
- — Irish
- “Oh, me virgin ears!”
- — Irish
- “You're an angry and a feck-ugly man, but not a bad one.”
- — Irish's last words to John Marston
- “It's the whisky, sir... It gives me the memory of a newborn babe. Innocent as could be.”
- — Irish
- In multiplayer, he is placed in the Damnation section, most likely due to his crimes, and attempts to get John killed, not to mention the nuns he tried to rob.
- If shot at before starting a mission, he may shoot back and possibly kill the player or simply run. During these moments, the player is unable to kill Irish.
- Irish's real name is never mentioned in-game.
- Irish seems to keep his revolver tucked into the front of his pants rather than in a holster.
- In multiplayer, Irish's gun is not in the front of his pants, but in a holster on his waist.
- When Irish puts his gun away after shooting in the mission "We Shall Be Together in Paradise", it uses the animation like he is putting his gun in a holster. His gun can then be seen to teleport to the front of his pants.
- After the mission "We Shall Be Together in Paradise", it is possible to kill him. However, the player needs to be extremely quick and likely will have to use Dead-Eye.
- He mentions indirectly that he met Landon Ricketts.
- Due to a comment Irish makes in "On Shaky's Ground", Irish may be from the city of Dublin, Ireland.
- He is one of the few original Red Dead Redemption characters that does not appear in Undead Nightmare. However on occasion a Retcher may be encountered which has a striking similarity to Irish and next to the train station in Armadillo, there is a half eaten corpse, that if looked at carefully, has a resemblance to Irish, with a Repeater Carbine next to the body.
- He appears to be a very well travelled person, having been to both Mexico and Canada, the majority of New Austin, and his native Ireland (then a part of the United Kingdom). These claims may be untrue, however, due to Irish's consistent dishonesty.
- Both of Irish's parents are mentioned at one point in the game. His father's throat was slit by a Welshman, as said in "A Frenchman, a Welshman and an Irishman", and his mother was still alive as of 1911, as said in "Man is Born Unto Trouble".
- Irish justifies his thievery with ideals very similar in concept to Marston's, as told by his dialogue with Marston after being caught threatening a pair of nuns for money in "On Shaky's Ground".
- Nigel West Dickens' relationship with Irish remains fairly ambiguous, considering he is rarely seen using heavy firearms. However, in dialogue, Irish mentions selling morphine to a friend named Shaky; Irish's drug trafficking may explain their relationship.
- Irish and the character Uncle are similar in many aspects, considering they both have very prominent beards, struggle with alcoholism, are fairly apathetic, only known by their nicknames, have similar facial structures and the type of "love/hate" relationship (although mostly hate) that Marston has with both.
- After completing "On Shaky's Ground", when Irish rides off, the player can catch up to him and get back on the wagon. Doing so will cause Irish to flee, and the player is able to kill or hogtie him.
- At the beginning of the mission Man is Born Unto Trouble, the song Irish is singing, "I love me precious Flora, the lily of the West", is in fact "Lily of the West", an old Irish folksong.