Jim Carrey, Ben Schwartz, Colleen O'Shaughnessey, James Marsden, Tika Sumpter, and Idris Elba reprise their roles, with Keanu Reeves joining the cast.

In the film, Sonic, Tails and Knuckles face Shadow the Hedgehog, who allies with the mad scientists Ivo and Gerald Robotnik to pursue revenge against humanity.

In Green Hills, Montana, Sonic celebrates the anniversary of his arrival on Earth with Tails, Knuckles, and their adoptive parents Tom and Maddie Wachowski.

Sonic and Shadow block the cannon's beam as Ivo, Tails, and Knuckles steer it away from Earth, accidentally slicing off part of the Moon.

When the cannon’s core begins to melt down, Ivo makes a final announcement acknowledging Stone as his only friend before he and Shadow sacrifice themselves to move it away from Earth before it explodes.

[9] Sofia Pernas and Cristo Fernández respectively play Gabriella and the twin brothers Juan / Pablo in La Última Pasión, a telenovela Ivo watches.

[11] Fowler said there was an "obvious corollary" between Reeves's performance in the John Wick series and the "vibe we're trying to channel" for Shadow, and thus these films served as a "perfect, albeit unconventional, 'audition'" for the character.

[41] Fowler attested that even if John Wick had never been made, he believed Reeves's established history with dark and edgy characters would have led to them casting him anyway.

[34] Additionally, Marsden, Ben Schwartz, Tika Sumpter, Colleen O'Shaughnessey, Idris Elba, Lee Majdoub, and Tom Butler were confirmed to reprise their roles from the previous films.

[20] Browne had previously been in George Miller's Three Thousand Years of Longing (2022) and Furiosa: A Mad Max Saga (2024) films, and Fowler said the team "inherited his great casting" of the actress.

[34] Casey said he and Miller had considered writing in the line "guns, lots of guns" for Shadow to say in an homage to voice actor Reeves having two characters, Neo from The Matrix and John Wick, who said the line before—though they decided against it, instead ending up with the film referencing the Reeves film Speed (1994) and the choreography of Sonic and Shadow's final duel mimicking that of Neo and Agent Smith's fight at the end of The Matrix.

[14] He acknowledged the elements of firearms and Shadow's motorcycle in his eponymous 2005 video game, and said that they were "very respectful about what fans expect to see and what they love about the character", and that he and his team were cognizant of how to properly incorporate that imagery into a family film.

[14] To write the dual roles of Gerald and Ivo for Carrey, Fowler said they initially focused on parallels between his two characters, "not just with bald heads and giant mustaches, but also in their behavior and their attitude"; they then decided they needed to "create the right sort of conflict" for the film.

[34] Miller described their role in writing the script for Carrey as building "an arena for him to kind of go bonkers and come up with all these ideas", and that much of the characters' humor was conceived by the actor himself, and Casey described this as a "framework".

[34] Second-unit filming began in late July 2023 for animated characters only without physical actors (due to the 2023 SAG-AFTRA strike) in Farnham, Surrey, England.

[16] Star Cristo Fernández said that he had not had the opportunity to meet his childhood hero Carrey nor Reeves during production, as his portion of the film was shot separately from all the other actors.

Owning the assets also allowed for their in-house team to work exclusively on Sonic the Hedgehog 3 and Knuckles, and helped the production "keep costs down and move faster.

[69] In April 2024 at CinemaCon, Paramount showcased first-look footage of the film, which featured a heavier Robotnik bemoaning his current state before Agent Stone informs him that "they found him", and Sonic, Tails, and Knuckles fighting a silent Shadow.

[78] Ash Parrish of The Verge agreed that Reeves's voice was satisfactory, and also noted Maria's reveal, anticipating how the film would adapt her fate.

[81] On November 18, a new poster was released, featuring the main team, the Robotniks, and Shadow, who looms above the cast at the top and also rides his Dark Rider motorcycle at the bottom.

[82] Several press outlets were also sent a Sega Genesis cartridge containing promotional posters and voice lines from the characters, as well as a minigame through which the date for the film's second trailer could be unlocked by inputting a cheat code from the game Sonic the Hedgehog 3 (1994); ↑ ↑ ↓ ↓ ↑ ↑ ↑ ↑.

[84][87] The phrases "HE HAS A GUN" and "HE PISSED ON THE MOON" began trending on social media following the trailer's release, with the latter being a reference to the popular web series SnapCube's Real-Time Fandub.

[93] A stop-motion short, "A Very Sonic Christmas", was released on December 11, 2024, with Schwartz, Elba, O'Shaughnessey, and Reeves reprising their roles, and Wade Whipple actor Adam Pally voicing Santa Claus.

[99] 4K SteelBook options include an edition with Sonic on the cover, and an Amazon retailer-exclusive version with Shadow on a red lightning bolt pattern background.

[7][8] In the United States and Canada, Sonic the Hedgehog 3 was released alongside Mufasa: The Lion King and was projected to gross $55–60 million from 3,800 theaters.

The website's consensus reads: "With a double helping of Jim Carrey's antics and a quicksilver pace befitting its hero, Sonic the Hedgehog 3 is the best entry in this amiable series yet.

Variety's Owen Gleiberman said that Reeves' "tones of deepest resonance" made Shadow empathetic to the audience, and that Jim Carrey topped his previous work with his roles as the Robotniks.

[3] Screen Rant's Rachel Labonte named Reeves's Shadow the standout of the film, saying the actor was brilliant at conveying the character's "hurt and steel".

[122] Polygon's Jesse Hassenger said Carrey's "gloriously deranged one-man, two-character musical" contrasted with the "utter sincerity" of Reeves, who made Shadow a "weirdly likable little ball of pain".

[130][131] Despite his character's apparent death in Sonic the Hedgehog 3, Carrey said in January 2025 that he was "open to the idea" of returning for the fourth film, provided that its premise interested him.