In the film, the Avengers and the Guardians of the Galaxy attempt to stop Thanos from collecting the six powerful Infinity Stones as part of his quest to kill half of all life in the universe.

The film received praise for Brolin's performance and the Russo brothers' direction, as well as the visual effects, action sequences, dark tone, emotional weight and musical score.

Having acquired the Power Stone—one of six Infinity Stones—from the planet Xandar, Thanos and his lieutenants—Ebony Maw, Cull Obsidian, Proxima Midnight, and Corvus Glaive—intercept the spaceship carrying the survivors of Asgard's destruction.

[b] Stark and Nebula remain stranded on Titan while Banner, M'Baku, Okoye, Rhodes, Rocket, Rogers, Romanoff, and Thor are left on the Wakandan battlefield.

Additionally, several other actors reprise their MCU roles: Danai Gurira as Okoye, the head of the Dora Milaje;[65] Letitia Wright as T'Challa's sister Shuri;[66] William Hurt as Thaddeus Ross, the U.S. Secretary of State;[67] Kerry Condon as the voice of Stark's AI F.R.I.D.A.Y.

[80][79] As Coon was pregnant during filming, she mainly did facial capture for Proxima Midnight with some motion-capture,[81] with stuntwoman Monique Ganderton standing-in and providing the rest on set.

[87] Executive producer Jon Favreau was to reprise his role as Happy Hogan, while co-director Joe Russo had a cameo appearance as a paparazzi photographer, but this scene did not make the theatrical cut of the film.

[107] For the film's final scene, where Thanos settles in a nipa hut, the filmmakers worked with Thailand-based studio Indochina Productions to acquire footage of the Banaue Rice Terraces at Ifugao, Philippines.

[118] Silvestri recorded his score from January 2018[119] to late March, and found working on the film to be "a really different experience than anything I'd done before, especially in regard to the approach and balancing quick shifts in tone".

[74] Additionally, Feige, Joe Russo, Downey, Brolin, Bettany, Olsen, Klementieff, Gillan, Bautista, Cheadle, Mackie, Cumberbatch, Stan, Holland, Boseman, Ruffalo, and Hemsworth appeared at D23 Expo to present a clip highlighting the 10 years of MCU films, along with footage from Infinity War.

[129] After the two convention presentations, Avengers: Infinity War generated over 90,000 new conversations on social media from July 17 to 23, the third-most during that time period behind Thor: Ragnarok and Justice League (2017), according to Comscore and its PreAct service.

[134] Josh Spiegel of The Hollywood Reporter said, "The most important part of the trailer is how it carefully, deliberately introduces the notion that the Infinity War films are going to function as a passing of the torch, from one set of Avengers to a newer group".

[140] A commercial for Infinity War aired during Super Bowl LII, and generated the most social media buzz of all the films advertised according to comScore and United Talent Agency; it was viewed 17.6 million times across YouTube and Facebook.

The week-long event saw stars from the film create social media challenges to provide funds and raise awareness for charities that support children and families impacted by serious illness.

The Russo brothers were fans of Fortnite and approached Donald Mustard, the worldwide creative director of Epic Games, about the potential for a crossover between the properties.

Lyga spoke with Marvel Studios to get an "outline of who Thanos is and what he means to the movies", and "was given great latitude and a free hand [in some areas of the story], while in others I had to tip-toe very carefully through the MCU".

The partners created television commercials "inspired by or featuring the film's characters and themes", interactive digital initiatives, and robust in-store presences at numerous retailers.

[162] Ahead of the United States release, AMC Theatres in New York City and Orlando, Florida aired an eleven-MCU film marathon beginning on April 25, ending in a screening of Infinity War.

The digital release also features a roundtable discussion between MCU directors the Russos, Jon Favreau, Joss Whedon, James Gunn, Ryan Coogler, Peyton Reed, and Taika Waititi.

[158] On June 12, 2018, Avengers: Infinity War passed the $2 billion mark at the worldwide box office, becoming the fourth film to cross that milestone after Avatar (2009), Titanic (1997), and The Force Awakens.

[178] Deadline Hollywood calculated the film's net profit as $500 million, accounting for production budgets, marketing, talent participations, and other costs; box office grosses and home media revenues placed it first on their list of 2018's "Most Valuable Blockbusters".

[179] Fandango later reported that Infinity War achieved the largest initial 24-hour ticket pre-sales for a superhero film, taking just 6 hours to surpass the previous 24-hour record set by Black Panther.

Atom also reported that ticket sales for Infinity War were doubling daily the week of its release, the fastest rate of increase the service has seen for any MCU title.

The website's critical consensus reads, "Avengers: Infinity War ably juggles a dizzying array of MCU heroes in the fight against their gravest threat yet, and the result is a thrilling, emotionally resonant blockbuster that (mostly) realizes its gargantuan ambitions.

[203] Todd McCarthy of The Hollywood Reporter praised the writers' and directors' ability to balance the large cast of characters, saying they, "under the supervision of Marvel Films maestro Kevin Feige, acknowledge the traffic jam of egos and play it for laughs".

[204] Owen Gleiberman of Variety concurred, stating, "Infinity War is a brashly entertaining jamboree, structured to show off each hero or heroine and give them just enough to do, and to update their mythologies without making it all feel like homework".

[205] McCarthy wrote, "Brolin's calm, considered reading of the character bestows this conquering beast with an unexpectedly resonant emotional dimension, making him much more than a thick stick figure of a supervillain".

[205] McCarthy called the scale of the action "astonishing",[204] and Travers wrote, "Avengers: Infinity War leaves viewers up in the air, feeling exhilarated and cheated at the same time, aching for a closure that never comes".

[206] Josh Spiegel, also of The Hollywood Reporter, said the film takes "a cue from the ending of The Empire Strikes Back in its super-sized finale; this is the equivalent of Han Solo frozen in the carbonite, on steroids".

[220][221] One Reddit user who participated described the ban as embodying "the spirit of the Internet" with people "banding together, en masse, around something relatively meaningless but somehow decidedly awesome and hilarious".