Hewlett was born in Redhill, England, and moved with his family to Canada at the age of four. Hewlett received his first computer in his mid-teens and became a self-described "computer nerd". While attending high school in Toronto, he launched his acting career, starring in student films by Vincenzo Natali. He dropped out of high school in his senior year to pursue careers in acting and computing, beginning his acting career in 1984 at the age of sixteen.
Hewlett has appeared in many low-budget horror films, such as The DarkSide and the minor cult favourites Scanners II: The New Order and Pin. He also guest starred in several television series. In 1996, he landed one of his better-known roles, as Grant Jansky on Traders. In 1997, Hewlett worked again with Natali, starring in the critically acclaimed thriller Cube as Worth the Architect, a role that saw the rise of his stardom due to the commercial success of the low budget Canadian film.
Hewlett married Actress Soo Garay in 2000. They divorced in 2004. He married Jane Loughman in 2008. Hewlett's younger sister is Actress Kate Hewlett. She has appeared on Stargate Atlantis as Rodney McKay's sister, Jeannie Miller, multiple times in the series. When he's not filming, Hewlett volunteers as a parent sponsor of a school PC/Tech club for kids interested in 3D printing, programming and re-purposing tech equipment.
In 2006, he wrote and directed A Dog's Breakfast starring himself, his sister Kate Hewlett, his dog Mars, and Stargate Atlantis costars Paul McGillion, Christopher Judge and Rachel Luttrell. In July 2006, Hewlett created a YouTube channel named Fanatical.
In 2007, Hewlett appeared as a guest star in the first episode of the TV series Sanctuary, a show produced by and starring Stargate Actress Amanda Tapping. He played Larry Tolson – a patient suffering from a form of Psychosis, who was shot and wounded before being taken into custody by police as a murder suspect.
In 2014, Hewlett directed the supernatural horror-science fiction film Debug with Jason Momoa, who starred alongside Hewlett in Stargate Atlantis. Jeananne Goossen and Adrian Holmes played the lead roles in the film.
In 2015, Hewlett appeared in the Syfy TV series Dark Matter, which is based on the comic book of the same name. He played a recurring role as Tabor Calchek, a merchant who also serves as the team's handler. Hewlett continues his interest in film making.
In 2017 he made HEWLOGRAM, a sci-fi comedy short showcasing the film making and special effects tools of Red Giant.
