Slade has been an automatic pick in the midfield for much of the last six years, appearing in 30 of the past 37 Tests since the 2019 tournament, but has been overlooked for the 33-man group.
Instead, the versatile Exeter centre has lost out to Joe Marchant, who covers wing as well as 13 and played his way into the squad after emerging from the wreckage of Saturday's defeat by Wales with his reputation enhanced.
The exclusion of Alex Dombrandt means that Billy Vunipola is the only specialist No.8 bound for France next month.
Dombrandt started every match in the Six Nations but was unable to stamp his authority on the jersey and compounded his humdrum form with an unimpressive display in Cardiff.
Vunipola is chosen despite not having played since April because of two knee surgeries and missing the entire Championship after being frozen out by Borthwick on form grounds.
Lewis Ludlam, Ben Earl and Tom Curry cover number eight and are present among a large contingent of versatile back five forwards that includes rookie Leicester duo Ollie Chessum and George Martin.
Other big names to miss out are wings Jonny May and Joe Cokanasiga, both of whom played in the World Cup four years ago.
"World Cups involve unique challenges in terms of the demands on players, the need for squad flexibility and the limited number of squad places available," Borthwick said.
"France 2023 is no different, but I'm confident we have selected a squad of 33 that is well able to meet those challenges and leave us best placed to be at our most competitive in this exciting tournament.
"There have been a number of very difficult selection decisions to make, given the quality of our wider training squad.
"Some very good players have missed out on selection such has been the competition for places over the last eight weeks and more of preparation."
England will meet Argentina in their opening Pool D fixture in Marseille on September 9.
Japan, Samoa and Chile are the other teams in the group.
ENGLAND RUGBY WORLD CUP SQUAD
Backs: Henry Arundell (Racing 92), Danny Care (Harlequins), Elliot Daly, Owen Farrell (both Saracens), George Ford (Sale Sharks), Ollie Lawrence (Bath), Max Malins (Bristol Bears), Joe Marchant (Stade Francais), Marcus Smith (Harlequins), Freddie Steward (Leicester Tigers), Manu Tuilagi (Sale Sharks), Jack van Poortvliet (Leicester Tigers), Anthony Watson (unattached), Ben Youngs (Leicester Tigers)
Forwards: Ollie Chessum, Dan Cole (both Leicester Tigers), Tom Curry (Sale Sharks), Theo Dan, Ben Earl, Jamie George (all Saracens), Ellis Genge (Bristol Bears), Maro Itoje (Saracens), Courtney Lawes, Lewis Ludlam (both Northampton Saints), Joe Marler (Harlequins), George Martin (Leicester Tigers), David Ribbans (Toulon), Bevan Rodd (Sale Sharks), Kyle Sinckler (Bristol Bears), Will Stuart (Bath), Billy Vunipola (Saracens), Jack Walker (Harlequins), Jack Willis (Toulouse).
- with Reuters
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