She was born as Helen Mary Boyd in Guildford, Surrey, England in November 1947 to Diana Frances Boyd and Colin Ian Langdon Boyd.

She was a freelance model in the 1960s, and often accompanied her sister Pattie to modelling jobs.

Despite Boyd being the inspiration of British folk musician Donovan's song "Jennifer Juniper", they have never been in a relationship, though Donovan admitted having a crush on her. The song was released as a single in March 1968 and on the album The Hurdy Gurdy Man later that year. Also in 1968, Boyd travelled with Donovan and her sister, Pattie Boyd, to Rishikesh, India, to attend a training session in Transcendental Meditation held by Maharishi Mahesh Yogi. Later Jenny shared an apartment with Magic Alex of Apple Corps's Apple Electronics subdivision. She also worked at the Apple Boutique in London.

Boyd was fifteen when she met Drummer Mick Fleetwood, who, at the time, was in a band called The Bo Street Runners and would later co-found Fleetwood Mac. From thereon, they began an on-and-off relationship that would last fifteen years. They eventually married in June 1970 and they had two daughters, Lucy and Amy. After divorcing Fleetwood (and remarrying and divorcing him a second time), Boyd married Drummer Ian Wallace in 1984 but they later divorced.

She attended UCLA in the late 1980s, earned a PhD in psychology, and became a clinical consultant and author. She co-authored a book about music and psychology, titled Musicians in Tune.