The midfielder was representing England Under-21s earlier this week and played 89 minutes in a 3-1 win against Czech Republic.
He has played for England at all levels from Under-17 to Under-21 – earning 36 caps – and will join Gareth Southgate’s squad before Monday night’s clash with San Marino. The Three Lions recently defeated Albania 5-0 in their first of two World Cup qualifiers this international break.
Speaking with cpfc.co.uk, Gallagher said: "I’m really happy and excited to be called up to the senior squad. I’m determined to make the most of the experience and know I have a lot of hard work to do.
"I’d like to thank everyone that has helped me in my career so far and I’ll do my best to make them proud."