First hired in New York by Andrew Ryan as his head building engineer, Bill McDonagh grew to become a key figure in the construction and founding of Rapture, as well as a close personal friend of Ryan's. McDonagh fought in World War 2, and moved from London to New York City after serving. As such, his character is featured with a strong cockney accent via a series of audio diaries found around Rapture in the original Bioshock game. These diaries chronicle McDonagh's transformation from being a dedicated and loyal servant of Andrew Ryan to a bitter, disenchanted citizen of Rapture seeking to kill his former friend and escape the city. His presence in the game is limited to these audio diaries and the player's exploration through Bill's bar, Fighting McDonagh's tavern.
McDonagh never partakes in plasmid use, although he must protect his wife Elaine and daughter Sophie as he witnesses Rapture's descent into chaos as splicers take over the city. Although his official job in Rapture is the head engineer and general contractor, Bill finds himself participating in raids against Frank Fontaine, brandishing weapons and killing numerous splicers in the process.
Bill's story climaxes with his attempted escape from Rapture, during which his resolve falters, causing him to pass up his opportunity to kill Andrew Ryan. He does, however, reach the surface with his family, where he is met by familiar members of Ryan's security force. Bill himself is returned to Rapture and executed, but his wife and child are allowed to escape, making them two of the only citizens of Rapture to successfully do so.
- "I met Ryan the day me and the lads were installing the bathroom plumbing up in his posh Park Avenue digs. 'Oi!' says he, 'what's with all the brass fittings? General contractor had me down for the tin.' 'Well,' I says, 'I supposed it's the contractor then who'll be bailing out your loo once a fortnight, is it? If it's price you're worried about, I'll be picking up the brass, so not to worry, squire.' 'And why would you be doing that,' says he? 'Well, Mr. Ryan, profit or not, no man bails water out of privies built by Bill McDonagh.' The next day I finds out, I'm Ryan's new general contractor."
- "If things weren't bad enough, it seems that even our water system's sprung a leak. Yep, that's right. The irrigation system in Arcadia is taking on sea water. I told Mr. Ryan when we were building this place; either you build her like a bathtub, or she's gonna turn into a sewer. "No, McDonagh," he said, "we're not gonna build no bathtub... we're gonna build Eden."
- "Seems like some poor blighters have started seeing ghosts. Ghosts! Ryan tells me it's a side effect of this Plasmid business. One poor sod's memories getting passed on to another through genetic sampling. Leaks. Lunatics. Rebellion. And now bleeding ghosts. Ain't life in Rapture grand?"