The 18-year-old was promoted from his country's Under-21s on Thursday and ended up coming off the bench for the closing stages of the 1-0 win over Luxembourg in a friendly at Windsor Park.
The match was an opportunity for coach O'Neill to blood some youngsters and Galbraith enjoyed getting his first taste of any senior competitive football in such an intense atmosphere.
“I'm lost for words,” Galbraith told BBC Northern Ireland. “It was absolutely unreal, especially in front of a big crowd and at Windsor Park. Even walking out in the stadium was incredible.
”Warming up on the side, I felt like everyone was just watching me and I was getting a bit nervous but then, when Michael gave me the call, the nerves went away and the adrenaline started kicking in, so it was good.