Former villain Gru is now an agent for the Anti-Villain League (AVL). He and his partner/wife Lucy are sent to foil the plans of Balthazar Bratt, a former child actor from the 1980s who has turned evil. Gru manages to stop Bratt from stealing the world's largest Diamond, but is unable to capture him. As a result of failing to capture Bratt, Gru and Lucy are fired from the AVL by its unreasonable new Director Valerie Da Vinci, following the retirement of Silas Ramsbottom.

Sandy Schaefer for Screen Rant gives the film a 3 out of 5 stars saying "Despicable Me 3 offers enough in the way of zany, irreverent entertainment (with a dose of heart) to please steadfast fans of the franchise." Jordan Mintzer for The Hollywood Reporter gave the film a positive review saying "This rather clever, breakneck-paced cartoon gives fans exactly what they want: Like the new nemesis voiced by Trey Parker, it shoots multiple machine-gun bursts of bubblegum at the audience, asking them to chew and enjoy" Peter Travers of Rolling Stone gave the film three out of four stars, saying "Pierre Coffin (who voices the Minions) and co-director Kyle Balda keep the plot spinning merrily. Pharrell Williams contributes five new songs to the mix, including the hummable "There's Something Special." It's no mystery why Illumination's franchise is still something special after three go-rounds – the box-office gross is a whopping $1.5 billion and counting."

On review aggregator Rotten Tomatoes, the film has an approval rating of 59% based on 174 reviews, and an average rating of 5.7/10. The website's critical consensus reads, "Despicable Me 3 should keep fans of the franchise consistently entertained with another round of colorful animation and zany—albeit somewhat scattershot—humor." On Metacritic, which assigns a normalized rating, the film has a score of 49 out of 100 based on 37 critics, indicating "mixed or average reviews". Audiences polled by CinemaScore gave the film an average grade of "A−" on an A+ to F scale, down from the first two films and the spin-off's "A".

The first official trailer for the film was released on December 14, 2016; with the second released on March 14, 2017. A secondary trailer, designed for TV usage was released on April 21, 2017. A third trailer was released on May 24, 2017.

Illumination's CEO Chris Meledandri has said in September 2017 that a fourth Despicable Me film is in development.

Leah Greenblatt of Entertainment Weekly gave the film a 'B' grade, saying "What shines through is the visual wit and innate sweetness of the storytelling, and Carell’s cackling, cueball-skulled misanthrope — a (mostly) reformed scoundrel who can still have his cake, and arsenic too." Stephen Whitty of the New York Daily News gave the film 3.5 out of 5 stars, saying "The film has to rush at the end, to wrap up all these different stories, and it still leaves one of them open-ended."