Liam Hemsworth was born on January 13, 1990, in Melbourne, Australia, and is the younger brother of actors Chris Hemsworth and Luke Hemsworth. He is the son of Leonie (van Os), a teacher of English, and Craig Hemsworth, a social-services counselor. He is of Dutch (from his immigrant maternal grandfather), Irish, English, Scottish, and German ancestry. His uncle, by marriage, was Rod Ansell, the bushman who inspired the film 'Crocodile' Dundee (1986).

The Hemsworth family lived primarily on Phillip Island, a small island located south of Melbourne. Following in the footsteps of his older brothers, who went into acting in their teens, Liam scored his first audition at age sixteen and appeared on the Australian TV series Home and Away (1988) and McLeod's Daughters (2001) before taking on a recurring character role on the soap opera Neighbours (1985), in which his brother Luke had also appeared. Roles on TV shows The Elephant Princess (2008) and Satisfaction (2007) followed before Liam moved to the United States to pursue a big-screen career.