Southgate initially named a provisional 33-man Euros squad last week, giving himself extra time to decide on his options before UEFA's deadline of June 1.
With Manchester United in the Europa League Final and Chelsea and Man City facing off in the Champions League Final, it also allowed Southgate time to assess any potential injury and fitness concerns for the players involved - but those involved all came through those games unscathed.
Euro 2020 - rescheduled from last year due to the pandemic - is less than a fortnight away, with England facing their first Group D game against Croatia on June 13.
They also have two warm-up games, starting with Austria on Wednesday and then Romania on Sunday.
When is the squad announced?
The Football Association will confirm all 26 names at 5pm BST.
England manager Gareth Southgate will host a press conference an hour later at 6pm BST.
Who is at risk?
Southgate will trim a talented squad of 33 down to 26 - and that's if the manager even decides to take the expanded number of offer, having previously suggested he preferred the initial 23-man complement.
Southgate's plans have also been complicated by not being able to work with a third of his provisional squad due to those continental cup final commitments.
His task got slightly easier on Tuesday morning with confirmation that Mason Greenwood has withdrawn after failing to shake up an injury.
Meanwhile, the fitness of Harry Maguire and Jordan Henderson are key considerations along with the balance of his group, especially given the strength in depth at right-back.
Whatever decisions Southgate makes, at least seven players - including Greenwood - will be axed from the group on the eve of Wednesday's warm-up friendly against Austria in Middlesbrough, where those already in camp will remain to aid preparations.
England squad (provisional)
Goalkeepers: Dean Henderson, Sam Johnstone, Jordan Pickford, Aaron Ramsdale
Defenders: Trent Alexander-Arnold, Ben Chilwell, Conor Coady, Ben Godfrey, Reece James, Harry Maguire, Tyrone Mings, Luke Shaw, John Stones, Kieran Trippier, Kyle Walker, Ben White
Midfielders: Jude Bellingham, Jordan Henderson, Jesse Lingard, Mason Mount, Kalvin Phillips, Declan Rice, James Ward-Prowse
Forwards: Dominic Calvert-Lewin, Phil Foden, Jack Grealish, Mason Greenwood, Harry Kane, Marcus Rashford, Bukayo Saka, Jadon Sancho, Raheem Sterling, Ollie Watkins