Morassi was born in Adelaide, South Australia, to Sandy and Liv Morassi. She lived in Adelaide until she was thirteen years old. She studied at the National Theatre, Melbourne Drama School, graduating in 1994, and another five years at Drama with a Difference.
Morassi has been in the Business for over a decade working in both local and international television, including BeastMaster, Stingers and The Secret Life of Us before making the transition to films in 2002 alongside an all-star cast including Bryan Brown, Toni Collette, Sam Neill, Sam Worthington, and John Goodman in Dirty Deeds which saw her nominated for a Best Supporting Actor award by the Film Critics Circle of Australia.
Morassi has also appeared in Darkness Falls, Travelling Light, Strange Bedfellows, Thunderstruck, The Illustrated Family Doctor, and Josh Jarman before getting her international break in the Australian box-office success Wolf Creek, which screened at the 2005 Sundance Film Festival. She played backpacker Kristy Earl, for which she was nominated for an Australian Film Institute award for Best Supporting Actress 2005. She also starred in the Patrick Hughes short film Signs for Schweppes opposite Nick Russell.
Morassi joined the cast of Seven Network soap opera Home and Away in 2017 as Maggie Astoni.
