Henstridge was born in Springdale, Newfoundland and Labrador on August 15, 1974, the daughter of Helen Henstridge, a homemaker, and Brian Henstridge, a construction manager and business owner. She was raised in Fort McMurray, Alberta, with her younger brother, Shane.
At age 14, Henstridge entered the Casablanca Modeling Agency\'s Look of the Year contest and was chosen first runner-up. The following year, she went to Paris to pursue her modeling ambitions. At age 15, she was featured on her first magazine cover, the French edition of Cosmopolitan. Several more magazine covers followed and Henstridge went on to do television commercials for products such as Olay, Old Spice and Lady Stetson. Her modeling career established, Henstridge started doing commercials and decided she preferred acting.
In her film debut Species (1995), Henstridge played Sil, a genetically engineered alien/human hybrid created from a message received by SETI, who breaks free from the captivity of a laboratory. Pursued by a team of experts who band together to stop her before she multiplies, Sil embarks on a killing spree while also discovering her powerful instinct to mate. Species was an instant hit, making US$113 million at the box office. Notable for its sexual content, the film won Henstridge the MTV Movie Award for Best Kiss for a scene in which her character, while kissing an aggressive would-be suitor, impales his head with her tongue. In 1998, she played Eve, a more ambiguous genetic duplicate of Sil, in Species II, which was a failure at the box office. Between Species films, Henstridge starred in two low budget action films in 1996, Adrenalin: Fear the Rush with Christopher Lambert, and Maximum Risk opposite Jean-Claude Van Damme.