The 26-year-old is eligible to play for them through his paternal grandfather, but initially missed out on a place in this month's squad as international clearance had not been granted.
FIFA subsequently confirmed the switch, with Scotland subsequently announcing that Hirst will join up with the group ahead of two big Nations League play-off games against Greece.
Steve Clarke's side travel to Piraeus on Thursday, March 20th (7:45pm), before hosting them at Hampden on Sunday, March 23rd (5pm).
Hirst, who scored off the bench in Saturday's 4-2 defeat to Nottingham Forest at Portman Road, has featured for England at every level from U17 to U20, although his last call-up came back in 2019.
He now looks set to earn his first cap for Scotland in the next fortnight, joining Town team-mate Cieran Slicker in their senior squad.
Cant wait to meet up with the boys💙 https://t.co/52QB7m69wq
— George Hirst (@GeorgeHirst45) March 16, 2025