She began acting in school plays in Grade 10 and graduated from Meadowvale Secondary School. She  She made the decision to pursue an acting career in her last year at Meadowvale and got the role in Never Have I Ever less than a year after. 

Maitreyi portrays Devi Vishwakumar, the lead role, in the Netflix series Never Have I Ever. In 2019, she was chosen by Mindy Kalling out of 15,000 candidates that applied for an open casting call for the show. Maitreyi created her audition tape at a local library, using her mother's camera, eventually being asked to send four more videos, before having a screen test in Los Angeles and being offered the role. Maitreyi was 17 at the time of her casting and had not yet held a job or acted professionally. Her casting received significant media attention, especially in Canada, both due to the nature ofthe open casting call and for her Tamil Canadian identity.

In 2019, Today named her one of eighteen "Groundbreakers", a list of girls who were breaking down barriers and changing the world. Her performance in the show received positive reviews, with Variety saying it was a "breakout performance".

In 2020, she narrated the Children's Programming portion of the 8th Canadian Screen Awards. In 2021, she was named as a Breakout Actor in Time 100's Most Influential people.