The uncapped 24-year-old has been in excellent form for the Bhoys this season and netted his 12th goal of the campaign in Sunday's 2-1 win at Dundee.
Gordon Strachan has clearly been tracking his progress and included him in his squad for Wednesday's friendly with Canada and Sunday's 2018 World Cup qualifier against Slovenia.
Armstrong was last called-up in August 2015, only to be forced out through injury but his time around he feels better prepared for the opportunity and is confident he is ready to make an impact on the international scene if given the chance.
"The last time I was called in was a while ago," he told Celtic's official website. "I had to pull out because of injury and it was a frustrating time. It has taken a while for me to get back in but that was in the past and this is now and I'm excited and looking forward to it.
"I'm a little bit older and experienced, especially with the Champions League experience and its pressures, and accepting the pressures of winning every week with Celtic and being happy with that."