The 21-year-old has been rewarded for an impressive start to the season which has seen him strike four times for the Scottish champions.
The news was confirmed by Scotland Under-21 coach Billy Stark, who has seen him promoted from his squad.
Stark said: "Andy Robertson has stepped up from the Under-21s and now Callum McGregor. Whilst it has not been the most successful of campaigns, the other part of it is players going through."
Dundee United midfielder Stuart Armstrong - who is Stark's captain - and Sheffield Wednesday striker Stevie May both have to be content with a place in the Under-21 squad for their double header against Slovakia and Scotland.
McGregor's promotion comes weeks after his Celtic breakthrough. The attacking midfielder has scored in each of Celtic's three away Champions League qualifiers and made himself a key player in Ronny Deila's early days as manager.
McGregor spent last season on loan at Sky Bet League One side Notts County, hitting 14 goals from midfield.
He comes in amid injuries to Robert Snodgrass and Scott Brown and fitness doubts over West Brom's James Morrison.
Stark named his squad before Gordon Strachan's selection for the September 7 clash in Dortmund was confirmed.
Stark added: "Club form obviously has a big part to that and Callum has had a great start to the season with Celtic so it's no surprise.
"I know Gordon has always liked the intelligence and football ability that he's got , so it's great for him."
Celtic goalkeeper Craig Gordon is also included in the squad following his comeback from a career-threatening knee injury.
Morrison has made the squad while Wolves midfielder Kevin McDonald is the only other uncapped player alongside McGregor.
Chris Burke, Shaun Maloney and Craig Bryson are among the other midfielders in Strachan's squad.
The Scotland manager has named three strikers - Steven Fletcher, Steven Naismith and Derby's Chris Martin - meaning there is no place for the likes of Jordan Rhodes, Ross McCormack or Leigh Griffiths.