According to Munro, her career took off in 1966 when her mother and photographer friend entered some headshots of her to Britain's The Evening News "Face of the Year" contest.

I wanted to do art. Art was my love. I went to Art School in Brighton but I was not very good at it. I just did not know what to do. I had a friend at the college who was studying photography and he needed somebody to photograph and he asked me. Unbeknownst to me, he sent the photographs to a big newspaper in London. The famous fashion photographer, David Bailey, was conducting a photo contest and my picture won.

This led to modelling chores, her first job being for Vogue magazine at the age of 17. She moved to London to pursue top modelling jobs and became a major cover girl for fashion and TV ads while there. Decorative bit parts came her way in such films as Casino Royale (1967) and Where's Jack? (1969). One of her many photo ads got her a screen test and a one-year contract at Paramount where she won the role of Richard Widmark's daughter in the comedy/western A Talent for Loving (1969).

1969 proved to be a good year for Munro, because it was then that she began a lucrative 10 year relationship with Lamb's Navy Rum. Her image was plastered all over the country, and this would eventually lead to her next big break.

1971 saw her appear alongside Vincent Price in The Abominable Dr. Phibes, playing the deceased Mrs. Victoria Regina Phibes:

The most challenging scenes involved lying in the coffin with Vincent," she reveals. "You see, I’m allergic to feathers and I was attired in this beautiful negligee — but it was covered with feathers! It took a great deal of willpower not to sneeze or sniffle. On occasion, I would simply have to sneeze and this would result in having to do another take.

She would reprise the role in the sequel, Dr. Phibes Rises Again in 1972. In the same year, she was referred to in Colin Blunstone's song "Caroline Goodbye", a song about the break-up of their relationship.

Hammer Films CEO Sir James Carreras spotted Munro on a Lamb’s Navy Rum poster/billboard. He asked his right hand man, James Liggett, to find and screen test her. She was immediately signed to a one-year contract. Her first film for Hammer proved to be something of a turning point in her career. It was during the making of Dracula AD 1972 that she decided from this film onward she was a full-fledged actress. Up until then, she was always considered a model who did some acting on the side.

Munro completed her contract for Hammer with Captain Kronos – Vampire Hunter in 1974. Directed by Brian Clemens, she plays the barefoot gypsy girl Carla. In Paramount Pictures DVD commentary, Clemens explains that he envisioned the role as a fiery, Raquel Welch type, red-head. Hammer pushed for Munro, and the script was adapted accordingly.

Munro has the distinction of being the only actor ever signed to a long-term contract by Hammer Films. She would later turn down the lead female roles in Hammer's Dr. Jekyll and Sister Hyde, Frankenstein and the Monster from Hell, and the unmade Vampirella because they required nudity.