Wildsmith was originally scheduled to play for the England under-20's during the current international break, but injuries have seen him move up the age groups.
Manchester City's Angus Gunn has withdrawn from the under-21 squad, and Gareth Southgate has quickly called Wildsmith into his team.
The 19-year-old is set to train alongside Sunderland's Jordan Pickford and Brighton & Hove Albion's Christian Walton this afternoon.
The under-21 call-up is reward for Wildsmith's form, which has been excellent for Wednesday throughout the campaign so far.
The Owls have played the youngster five times in all competitions so far this season, with optimism high about his future at Hillsborough.
Wildsmith has never played for the under-21 side before, but he did make an appearance for the under-20's in their most recent game against Holland, which they won 3-1.