But Cassin says there was a niggling doubt. "I also loved singing Motown and soul and I wasn't allowed to sing those things anymore, because I had to reserve my voice for classical.
And that really upset me. I realised opera didn't resonate with me as a person - the voice could go there, but my music personality wasn't fitting the mould."
Disenchanted with singing, Cassin's career took a sharp turn. "I went and studied counselling - something completely different," she laughs.
Today, Cassin is back in the game. But this time, it's on her terms. She recently released her debut single Slow and is working on getting the funds to release her EP, Kin.
"It is electronic, but with a bit of a neo-soul influence. It has a mellow feel to it, a bit of a James Blake feel to it - very atmospheric. I always aim for a mood," she says of her sound.
"There are quite abstract concepts in my songs. There's definitely an intimacy in my writing - a vulnerability."
Cassin hasn't got a firm date on the EP's release yet and says the priority now is to get her music out there and play gigs as a way of introducing herself, starting with a performance at Auckland's Golden Dawn on July 25.
There's plenty else to keep her busy too, including her involvement in musical theatre groups such as the Blackbird Ensemble and in a few months, she will be off on a European tour with Sola Rosa.
It's all exciting stuff and still early days for the 28-year-old singer who could have so easily continued down the classical path.
But Cassin says there are no regrets. She just hopes that her sound is something people will enjoy. "I hope it makes someone's day," she says with a smile.
• Jessie Cassin's new single Slow is out now. She's performing at Golden Dawn in Ponsonby on July 25.