Rathbone was born in Singapore, the son of American parents Randee Lynn (née Brauner) and Monroe Jackson Rathbone IV.   His great-grandfather, Monroe Jackson Rathbone II, was the chairman of Standard Oil of New Jersey, which later became Exxon ;  Rathbone is distantly related to Civil War general Stonewall Jackson and British actor Basil Rathbone.  Because of his father's job at Mobil Oil, Rathbone has lived in places ranging from Indonesia to Midland, Texas.  He attended Trinity School of Midland, a college preparatory school, and started out in local theater in Midland with the youth actors program "The Pickwick Players", initially doing musical theatre.  For his junior and senior years of high school, Rathbone attended the Interlochen Arts Academy, a private school for the arts in Michigan, where he majored in acting.   After graduation, he had planned to go to the Royal Scottish Academy of Music and Drama, but went instead to Los Angeles to experiment with film acting. 
After being in Los Angeles for a short time, Rathbone was cast in Disney 411 , where he interviewed up-and-coming personalities like Hilary Duff and the sister duo Aly & AJ. He also had guest roles on The O.C. and Close to Home . His film roles include work in Molding Clay , Pray for Morning , and Travis and Henry . In 2005, he got the role of Nicholas Fiske in ABC Family's original series Beautiful People . In a 2008 interview, he stated it was his first leading role and was his most difficult role to fit into.  Rathbone also played a role in Criminal Minds as Adam and Amanda.
In 2008, he played Jasper Hale in the film Twilight, based on the best-selling novel by Stephenie Meyer.  He reprised his role in the sequels to Twilight , The Twilight Saga: New Moon , The Twilight Saga: Eclipse and The Twilight Saga: Breaking Dawn .   In 2009, Rathbone played Jeremy in S. Darko . In addition to that role, he won kudos for his performance as a serial killer on Criminal Minds . Rathbone played the role of Sokka in The Last Airbender , a 2010 film based on the animated series. 
Rathbone appeared in an episode of No Ordinary Family on November 9, 2010.   In November 2010, it was reported he had been cast in the Warner Premiere and Dolphin Entertainment action webseries Aim High alongside Aimee Teegarden.   The show in which he portrays Nick Green, a high school junior who's just starting a new school year as one of the country's 64 highly trained teenage operatives, premiered on October 18, 2011, on Facebook being the first "social series" ever created. 
In May 2011, Rathbone began shooting Live at the Foxes Den , a film in which he plays the lead role of lawyer Bobby Kelly.
In November 2014, Rathbone joined the cast of Pali Road .
Rathbone has a production company, PatchMo Entertainment, and a record company, Happy Jack Records.
Rathbone enjoys music, writing, singing and producing.  He formerly performed in a band called 100 Monkeys with two friends whom he met in high school at Interlochen Arts Academy, Ben Graupner and Ben Johnson,  as well as close friends Jerad Anderson and M. Lawrence Abrams ("Uncle Larry").  The band released three albums in 2009.  In December 2009, 100 Monkeys began a 100-city tour that took them to nearly every state in the US by mid-2010.  The band continued to tour into 2011 to coincide with the release of their new album, Liquid Zoo , which was released in June.  The band headed overseas for their first international dates in winter 2011. 
Rathbone resides in Los Angeles.
Rathbone and his then girlfriend, Sheila Hafsadi, had a son, Monroe Jackson Rathbone VI, on July 5, 2012.  Close friend and Twilight co-star Nikki Reed is the godmother. He and Hafsadi married on September 29, 2013.    On May 31, 2016, he and Hafsadi welcomed their second child, a daughter named Presley Bowie Rathbone. 
On September 18, 2014, Rathbone was on board JetBlue Flight 1416 en-route from Long Beach, California to Austin, Texas when its engine exploded. The plane returned to Long Beach and performed an emergency landing with all passengers surviving and four injuries.  
Rathbone is an honorary board member for Little Kids Rock, a national nonprofit that works to restore and revitalize music education in disadvantaged U.S. public schools. He has shown support for the organization in several ways, including donating a signed Twilight script for auction, visiting a Little Kids Rock classroom, and delivering instruments to students.
|Close to Home||Scott Fields||TV series|
|2006||Pray for Morning||Connor|
|O.C., The The O.C.||Justin Edwards||TV series, episodes: " The Sister Act " and " The Heavy Lifting "|
|Beautiful People||Nicholas Fiske||TV series|
|2007||Valley of Light, The The Valley of Light||Travis|
|War at Home, The The War at Home||Dylan||TV series|
|Big Stan||Robbie the Hippie|
|2008||Senior Skip Day||Snippy|
|Cleaner, The The Cleaner||Joey||TV series, episode: "Back To One"|
|2009||DaZe: Vol. Too (sic) - NonSeNse||Jehosefat|
|S. Darko||Jeremy Frame|
|Criminal Minds||Adam Jackson||TV series, episode: "Conflicted"|
|Twilight Saga: New Moon, The The Twilight Saga: New Moon||Jasper Hale|
|2010||Last Airbender, The The Last Airbender||Sokka|
|Twilight Saga: Eclipse, The The Twilight Saga: Eclipse||Jasper Hale|
|No Ordinary Family||Trent||TV series, episode: "No Ordinary Visitors"|
|2011||Twilight Saga: Breaking Dawn – Part 1, The The Twilight Saga: Breaking Dawn – Part 1||Jasper Hale|
|Aim High||Nick Green||Web series (2011–2013), 16 episodes|
|2012||Zombie Hamlet||Shakespeare Purist||uncredited|
|Cowgirls n' Angels||Justin Wood|
|Twilight Saga: Breaking Dawn – Part 2, The The Twilight Saga: Breaking Dawn – Part 2||Jasper Hale|
|2013||White Collar||Nate Osbourne||TV series, episode "Shoot The Moon"|
|NTSF:SD:SUV::||Jesse James||TV series, episode " The Great Train Stoppery "|
|The Magic Bracelet||Geoff||Short film|
|Live at the Foxes Den||Bobby Kelly|
|City of Dead Men||Jacob|
|2016||Pali Road||Neil Lang|
|2017||The Last Ship||Giorgio|
|Until We Meet Again||Eddie Conway|
|Horseshoe Theory||Bobbo||Short film|
|2018||Samson (2018 film)||Rallah|