Meryl wanted to become an actress ever since she was 5 years old. She has trained in drama at the Young People's Theatre and Nathan Homestead. Because she wanted to get into acting as soon as possible, she got an agent at the age of 9, as she saw this as the first and best option to achieve her goal. Meryl got her first acting job in the New Zealand kids show What Now at the age of 11, where she starred as a field presenter. In 1998, Meryl auditioned for the show that would give her both success and acting experience: The Tribe. She auditioned for the goodie character Salene, but the producers called her and told her she had got the character of Ebony, one of the meanest characters the show would ever see. Official filming of the first season commenced in August 1998, and lasted for six months to March 1999. The fifth and last season wrapped up principal photography on March 1, 2003. In the period of 2004 to 2007, Meryl went on a hiatus, and took a break from acting and singing. She worked in a bank, helped out at her mother's hair braiding salon and gave birth to her first child, Rylon Ngarino Watt, on September 16, 2006. In 2004, she auditioned for New Zealand Idol. She did not make it past the second round, partly because the judges thought she had too much experience to be in the contest. Various reports have stated that Cassie was very sad and actually cried on camera, saying how mean the judges were. Meryl's brother, Miguel Cassie, was going to make a TV documentary about Idol, where the rejected contestants could have a new chance. This show never saw the light of day. In 2006 Meryl Cassie provided music for NZ teen series Karaoke High. Though she didn't appear on the show, she provided her singing talent for the character Miri (played by Alina Transom).In 2008 Meryl appeared in the music video for P-Money's "Everything", where she was dancing on the shoulders of the lead female in the music video. She also sang an impromptu performance of the Kelly Clarkson track 'A Moment Like This' at a reunion of members of The Tribe cast, which was held on 13 September 2008. She ended the year performing on stage at the Coca-Cola Christmas In The Park 2008, where she sang "What Time Is It?" with fellow New Zealand entertainers Drew Neemia, Catherine Campion, Anthony Utama, Cameron Douglas & Jodie Clarke. Following on on from her appearance in P-Money's music video 'Everything' in 2008, Meryl became the lead in his music video 'Angels' where she plays the girlfriend of P-Money's who is being haunted by supernatural beings. 2010 she plays as Stacy Butler/Yellow Samurai Strike Ranger in power rangers samurai strike.
She is a mother to a two year old son named Rylon.