Pre Production

On September 2012, Gunn confirmed that he had signed on to direct the film and rewrite the script. By the end of November, Joel Edgerton, Jack Huston, Jim Sturgess, and Eddie Redmayne signed deals to test for the role of Peter Quill, as did Lee Pace, which he confirmed a week later in early December.Other actors who were considered for the role included Thor: The Dark World 's Zachary Levi,Joseph Gordon-Levitt, and Michael Rosenbaum. Chris Pratt was cast in the role in February 2013, as part of a multi-film deal that he signed with Marvel.

In January 2013, filming was scheduled to take place at Shepperton Studios in London, United Kingdom,and Marvel Studios announced that the film would be released in 3D. Victoria Alonso, an executive producer on the film, said that filming would begin in June. She also said that both Rocket Raccoon and Groot would be created through a combination of CGI and motion capture, going on to say that "You can't do any motion capture with a raccoon – they won't let you put the suit on. But we will do rotomation, probably, for some of the behavior... we definitely will have performers to emulate what James Gunn will lead to be, the behavior and the performance. He's very clear on where he wants to take the characters." In March 2013, Feige discussed Guardians of the Galaxy in relation to the Marvel Cinematic Universe, saying, "It's much more of a standalone film. It takes place in the same universe. And when we've been on the other side of that universe in other movies, you might see those characteristics in Guardians, but the Avengers are not involved with what's happening out there at this time." Feige also stated that 95% of the film would take place in space. In mid-March, Dave Bautista was signed to play Drax the Destroyer. Other actors who had been considered for the role included Isaiah Mustafa, Brian Patrick Wade and Jason Momoa. By the following week, sculptor Brian Muir, who sculpted Darth Vader's mask for the Star Wars films, was revealed to be working on the film.

In early April 2013, Zoe Saldana entered into negotiations to star as Gamora in the film, and it was confirmed she had been cast later that month.Also in April, Michael Rooker joined the film's cast as Yondu, and it was announced that Ophelia Lovibond had been cast in a supporting role.By this point in time, Lee Pace was in final negotiations to play the villain of the film. In May, Marvel offered John C. Reilly the role of Rhomann Dey.At the same time, it was disclosed that filmmakers were looking at actors including Hugh Laurie, Alan Rickman, and Ken Watanabe, for another role, and that Christopher Markus and Stephen McFeely were providing finishing touches to the script. A few days later, Glenn Close was cast as the head of the Nova Corps in the film, followed shortly by the casting of Karen Gillan as the film's lead female villain.By June 2013, Benicio del Toro was cast in the film, as part of a multi-film deal with Marvel Studios. Later in the month, it was confirmed that Reilly had been cast as Rhomann Dey.

Special effects makeup designer David White took head and body casts of actors, such as Bautista, to experiment with materials used to create the characters. White said, "James always pushed for practical and makeup effects. He wanted, like me, to see the real deal there on set." White was careful not to use "modern" creature designs to ensure they did not fall short in Gunn's uniquely envisioned world. White and his team created upwards of 1,000 prosthetic makeup applications and 2,000 molds of different colored aliens.For the specific aesthetic look to the film, Gunn wanted to create "a colorful science-fiction world", and include elements of 1950s and 60s pulp movies, citing the Ravagers' spaceships, which he compared to muscle cars, as an example of the latter.