The Three Lions have already handed Brighton and Hove Albion centre-back Lewis Dunk a first worldwide call-up as well after James Tarkowski suffered an injury setback.
"The Leicester City defender, who won his first cap in last month's win over Switzerland, was initially called up by the Under-21s but will now travel to Croatia and Spain later this week".
Southgate's side face Croatia in Rijeka on Friday as they look to exact some revenge for their World Cup semi-final defeat during the summer, with the Nations League clash at Stadion HNK to be played behind closed doors before a trip to face Spain in Seville on Monday evening.
Shaw played full 90 minutes in United's weekend 3-2 comeback win over Newcastle but reportedly played the full game with a minor knock.
Dunk's maiden call-up comes a week after the 26-year-old signed a new five-year deal with the Seagulls.
"I'm delighted he has now been given recognition at worldwide level".
Chilwell adds to an already inexperienced squad assembled by Gareth Southgate with his Leicester team-mate James Maddison, 21, on loan Derby midfielder Mason Mount, 19, and Borussia Dortmund's Jadon Sancho, 18, all receiving their first call-ups.