The 32-player line-up was finalised following the conclusion of Players Championship 24 in Leicester on Tuesday. It comprises the top 16 players from the world rankings, who are seeded, and the top 16 players from the one-year ProTour rankings, who qualify unseeded.
The players will compete for the Phil Taylor Trophy in an event with a total prize fund of £1 million.
Littler, the world champion, is bidding to become only the fourth player to retain the World Matchplay title, following Phil Taylor, Rod Harrington and Michael van Gerwen. He won last year's final 18-13 against James Wade, having trailed 5-0 at one stage.
Luke Humphries, champion in 2024, is seeded second. Dutch number one Gian van Veen is seeded third, with three-time champion Michael van Gerwen fourth. Jonny Clayton and James Wade are seeded fifth and sixth, with Gerwyn Price and Josh Rock completing the top eight.
Stephen Bunting, Danny Noppert, Ryan Searle, Gary Anderson, Chris Dobey, Wessel Nijman, Ross Smith and Nathan Aspinall make up the remaining seeded places.
Luke Woodhouse heads the 16 ProTour qualifiers after finishing runner-up to Gabriel Clemens in the Players Championship 24 final.
Jermaine Wattimena, Kevin Doets and Rob Cross are among the other qualifiers, with Doets, William O'Connor, Niko Springer and Niels Zonneveld all set to make their World Matchplay debuts.
Dave Chisnall secured the final qualifying spot on the last day of eligibility, extending his run of consecutive World Matchplay qualifications to 16 years. His qualification came at the expense of Daryl Gurney, who was beaten in the first round of Players Championship 24 and will miss the tournament for the first time since 2015.
Peter Wright, the 2021 champion, also failed to qualify, missing out for the first time since 2012.
The full list of ProTour qualifiers is completed by Andrew Gilding, Krzysztof Ratajski, Martin Schindler, Ryan Joyce, Dirk van Duijvenbode, Cameron Menzies, Joe Cullen and Damon Heta.
The draw for the tournament will be made on Thursday, July 9th, with each seeded player drawn against one of the 16 ProTour qualifiers in the first round.