The young Irishman, formerly of Bohemians, has signed a contract until the end of the 2025/26 season, with an option to extend for a further year.
The 20 year-old told the club's website: “It’s an absolutely wonderful feeling.
“It's hard to put into words. I've had a tough time with injuries over the last few years, so to be given a chance at such a massive Club is something I’ll forever be grateful for. I can't wait to get started and kick on, hopefully, please God.
“To be back at a Club like West Ham, I’m lost for words. I’m quite emotional, because it means that extra bit more. I want it more than I did before. It’s almost like a second coming for me, because six months ago I didn’t know where I was going to be.
“It was a tough personal period, but to be given the trust and guidance from the Club here, to feel wanted, is really special and makes me feel good about myself.
“It’s been a really smooth process. The staff and the lads helped me settle in and feel comfortable from day one, even when I was on trial. I’ve got nothing but high praise for the staff, and especially Bill (Lepine), who’s taken me under his wing and given me a platform to impress.”