Nothing is known of Diarmuid's background. He has a slight Irish accent and common Irish name, hinting that he may have been born in Ireland, but immigrated to the United States when he was younger.
Diarmuid can most often be found in Thieves' Landing, loitering in and around the Saloon or brothel. He commonly plays Poker and Liar's Dice. He also frequents the town of Blackwater, as well as other locations throughout West Elizabeth and New Austin.
|—Diarmuid O'Keefe during a fight|
|“||Jesus, Mary, and Joseph! Somebody get help!||„|
|—Diarmuid O'Keefe' after being shot|
|“||It's John Marston. Hello, John.||„|
|—Diarmuid O'Keefe greeting the player|
|Hey there, cowboy. This article looks a little bit small.|
I reckon you could impress me by contributing to it. Don't be shy now.