Hemsworth was born in Melbourne, Australia. He is the son of Leonie, a teacher of English, and Craig Hemsworth, a social-services counselor. He has two older brothers, Chris and Luke Hemsworth, who also work as actors. Hemsworth has said that though there is competition for jobs among them, it is friendly: "We are brothers and we are always competitive, but it is a good thing, it pushes us and we are always happy whenever someone books something."
When Hemsworth was in year 8, he and his family relocated to Phillip Island, a small island. Hemsworth says he spent much of his time there surfing with his brothers. In March 2009, Hemsworth moved to the United States to pursue his career there. He and his brother Chris first stayed in the guest house of Chris's manager, William Ward, before renting their own Los Angeles apartment.
Prior to becoming an actor, Hemsworth laid floors for six months. He began to seriously consider following his elder brothers' footsteps in high school by participating in school plays. Eventually, Hemsworth retained an agent. He attended his first audition at the age of sixteen and began his career in 2007 with guest spots on the shows Home and Away and McLeod's Daughters. The week of 8 July 2007, Hemsworth began filming episodes for Neighbours, an Australian soap opera his brother Luke had previously starred in. Hemsworth's character, Josh Taylor, was a recurring character from 2007 to 2008. In the show, Josh was an athletic paraplegic who supported and began a relationship with character Bridget Parker after she was paralysed down one side of her body in a car crash. In 2008, Hemsworth began acting on the children's television show The Elephant Princess, playing "Marcus", the attractive lead guitarist of the protagonist's band. Hemsworth later had roles in the television series Satisfaction and starred in the British film Triangle. He also made a brief appearance as an MIT student in the film Knowing.
In 2009, Hemsworth was selected to act opposite Sylvester Stallone in Stallone's 2010 film, The Expendables, but his character was written out of the script (Hemsworth later co-starred in The Expendables 2). Hemsworth's brother, Chris, told Movieline that just a few hours after Hemsworth learned he would not appear in The Expendables, director Kenneth Branagh called to ask him to test for the lead role in the 2011 film Thor. Hemsworth moved to the States in March 2009 for screen tests. Though he eventually lost the part to Chris in May, Disney announced later the same week that Hemsworth had landed the part of Will Blakelee in the 2010 drama The Last Song, based on the Nicholas Sparks novel by the same name. Hemsworth plays the love interest of Miley Cyrus's character in the film. Nikki Finke reported that Hemsworth had been in Los Angeles for just three weeks and had not yet found an agent when he was cast. Hemsworth next appeared in the music video for Cyrus' "When I Look at You" which was recorded on 16 August 2009.
In September 2009, Hemsworth appeared at a dinner event to promote Foxtel, an Australian pay television company. In March 2010, Details magazine selected Hemsworth as one of their predictions for "The Next Generation of Hollywood's Leading Men". Later that month, it was announced that Hemsworth was in negotiations to star in Arabian Nights, a 3D action film that will be directed by Chuck Russell for Inferno Entertainment. It was later confirmed that he will be starring in the movie. He has also reportedly been offered the lead role in "Northern Lights" after "Twilight" star Taylor Lautner withdrew from the David Ellison-financed project.
Hemsworth was the Nickelodeon Australian Kids' Choice Awards 2010 host. He and Miley Cyrus won the "Fave Kiss" category.
Hemsworth stars in the music video Colder Weather for Zac Brown Band.
On 4 April 2011, Lionsgate announced Hemsworth to be one of the leads, Gale Hawthorne, in The Hunger Games, which was released in 2012. In June 2011, he became attached to war drama Love and Honor which also stars Aimee Teegarden and Teresa Palmer.
In 2013, Hemsworth will appear in Empire State with Emma Roberts, Paranoia co-starring Harrison Ford and Timeless as a widower who travels back in time. He will reprise his role as Gale Hawthorne in the sequel to The Hunger Games called The Hunger Games: Catching Fire, set to be released in November 2013.
While filming The Last Song in June 2009, Hemsworth began a relationship with his co-star Miley Cyrus. In August 2010, it was confirmed that his relationship with Cyrus had ended. Cyrus and Hemsworth were seen together a month later, and had reportedly reconciled. It was announced in early November that the couple had split again, but reconciled their relationship a second time. In 2012, the couple announced their engagement.
Hemsworth is the ambassador of the Australian Childhood Foundation. Hemsworth talked about his association with the foundation, "I have the best parents you can have. They have worked in child protection for twenty years and have only ever given me encouragement and support. The world is a scary enough place as it is for children. It is important that home should always be a safe place for them." When asked if he believed he was a hero to children, Liam said he did not know, but that he would like to be a good role model.