The 18-year-old is one of five youngsters who have been given maiden call-ups for next month's European Championship qualifying double-header away to Denmark and Belgium.
Lowry has scored twice in seven appearances for Rangers since making his debut in January and was an unused substitute in Wednesday's Europa League final defeat by Eintracht Frankfurt.
"I haven't worked with Alex yet but I've really enjoyed watching him get his opportunity with his club," said head coach Gemmill. "He did really well for the (Scotland) under-19s and I'm really excited to give an exciting, highly-regarded young player an opportunity to play at this level.
"He's the same as all the players, he has to come and really maximise the opportunity and show he can play at this level."
Rangers' Leon King, Dundee United's Archie Meekison and Dundee pair Josh Mulligan and Harrison Sharp are the four other new call-ups for a formidable double-header away to the two top teams in the group.
Scotland are out of contention for qualification but Gemmill hopes his team can rise to the challenge.
"The players will be well prepared," he said. "They have to show they've got the intelligence and application to play at this level and understand that it's not just about them, it's about the team.
"There will be demands from the staff in terms of application and having the right mentality and playing at the right intensity.
"A lot of the young players come and play at this level for the first time and speak about how fast it is.
"You only have to look at the level of the opposition players - it really is best v best. It's a big challenge but I'm sure they're all looking forward to it."
Scotland Under-21 squad: Sam Long (Drogheda United), Harrison Sharp (Dundee), Ross Sinclair (St Johnstone), Harrison Ashby (West Ham United), Thomas Clayton (Liverpool), Ross Graham (Dundee United), Leon King (Rangers), Lewis Mayo (Rangers), Stephen Welsh (Celtic), Elliot Anderson (Bristol Rovers), Connor Barron (Aberdeen), Jack Burroughs (Coventry City), Jay Henderson (St Mirren), Scott High (Huddersfield Town), Stephen Kelly (Rangers), Marc Leonard (Brighton and Hove Albion), Alex Lowry (Rangers), Archie Meekison (Dundee United), Josh Mulligan (Dundee), Connor Smith (Heart of Midlothian), Glenn Middleton (St Johnstone), Dapo Mebude (AFC Wimbledon)