Garrett John Hedlund was born on September 3, 1984, in Roseau, Minnesota, to Kristine Anne (née Yanish) and Robert Martin Hedlund. He is the youngest of three children, with a brother, Nathaniel, and a sister, Amanda. His father is of Swedish descent and his mother is of Norwegian and German descent. Hedlund was raised on a remote beef cattle farm near the small town of Wannaska, Minnesota in the Scandinavian diaspora.

In 2003, Hedlund moved to Los Angeles to pursue his acting career. As a teenager, Hedlund modeled for L.L. Bean and Teen Magazine.

Hedlund, at the age of 19, debuted in his first feature film playing Brad Pitt’s younger cousin Patroclus in the mythological epic adventure war drama Troy. The film was released on May 14, 2004. He also co-starred with Billy Bob Thornton, Amber Heard and Tim McGraw as Don Billingsley in the 2004 sports drama Friday Night Lights, where McGraw played his abusive father. He co-starred with Mark Wahlberg in the crime drama Four Brothers as Jack Mercer.

He co-starred with Ed Speleers, Jeremy Irons, Sienna Guillory and John Malkovich in the fantasy-adventure film Eragon as Murtagh. In October 2006, it was announced that the actors from the Eragon film would lend their voices to the game adaptation. Hedlund lends his image and voice to his character Murtagh in the video game Eragon.

In 2007, he co-starred with Lindsay Lohan, Jane Fonda and Felicity Huffman in the comedy-drama Georgia Rule, directed by Garry Marshall. That same year, he co-starred with Kevin Bacon in the crime thriller Death Sentence, directed by James Wan.

In 2010, he co-starred with Jeff Bridges in the science fiction/action film Tron: Legacy, playing Sam Flynn. Hedlund won a “Darwinian casting process” which tested hundreds of actors, being chosen for having the “unique combination of intelligence, wit, humor, look and physicality” that the producers were looking for in Flynn’s son. Hedlund trained hard to do his own stunts, which included jumping over cars and copious wire and harness work. The film was released on December 17, 2010 and directed by Joseph Kosinski. It is a sequel to the 1982 film Tron, whose director Steven Lisberger returned to produce.

Hedlund co-starred with Gwyneth Paltrow, Leighton Meester and his Friday Night Lights co-star, country musician Tim McGraw in the musical drama Country Strong, which was released on December 22, 2010. He recorded a number of songs for the film including “Chances Are” which appeared on Country Strong: Original Motion Picture Soundtrack. His performance was well received by critics. Noting voice similarities between Hedlund and Charlie Robison, Roughstock said “the best song on this album belongs to him” and Country Weekly wrote that of all the songs performed by actors in this film, his was “the most convincing”. Six other songs, including a duet with Meester, were featured on a second soundtrack titled Country Strong: More Music from the Motion Picture.

He also co-starred with Kristen Stewart, Sam Riley, Kirsten Dunst and Viggo Mortensen as Dean Moriarty in the 2012 adventure drama On the Road. The film was directed by Walter Salles and based on Jack Kerouac’s novel of same name. Hedlund was cast as Kaneda Shotaro in the live-action version of Akira but production of the film was cancelled. In 2012, he was an advertising and catwalk model for the Italian fashion firm Prada. Disney said in December 2012 that Hedlund would reprise his role of Sam Flynn in the sequel to Tron: Legacy.

He co-starred with Oscar Isaac, Justin Timberlake and Adam Driver in the 2013 French-American black comedy-drama film Inside Llewyn Davis, directed by Joel and Ethan Coen. Hedlund pays homage to a fallen Cowboy whose name is Lane Frost in the music video of the song Beautiful War by American rock band Kings of Leon. In 2013, he was also the image of Yves Saint Laurent Beauté’s French men’s fragrance “La Nuit de l’Homme”.

In 2014, Hedlund co-starred with Jack O’Connell and Domhnall Gleeson in the historical drama Unbroken, directed by Angelina Jolie. In 2015, he plays James Hook (future Captain Hook) in the film Pan, co-starring alongside Hugh Jackman and Rooney Mara, directed by Joe Wright. In September of that same year, Hedlund wrote the book Art of Pan with Joe Wright and Christopher Grove. He co-starred with Joe Alwyn and Vin Diesel the 2016 film war drama film Billy Lynn’s Long Halftime Walk, directed by Ang Lee. In 2017, he co-starred with Carey Mulligan the film Mudbound, directed by Dee Rees.

He co-starred with Forest Whitaker and Usher in the 2018 drama film Burden, inspired by true events. In 2019, he co-starred with Ben Affleck in the action-adventure film, released by Netflix, Triple Frontier recorded between Soacha and Bogotá, where he plays a ex SEAL in a particular mercenary operation in South America. He co-stars with Kelly Macdonald in the romantic drama film Dirt Music, directed by Gregor Jordan, based on the novel of the same name by Tim Winton.

As of March 2019, Hedlund is dating actress Emma Roberts. In August 2020, it was announced that the couple were expecting their first child, a boy.