Jennifer Lee O’Neill was born on February 20, 1948, in Rio de Janeiro, Brazil, to Irene Freda Pope, a London-born mother, and Oscar Delgado O’Neill, a Brazilian of Portuguese, Spanish, and Irish ancestry who worked in medical supplies and had served as a bomber pilot in the Second World War.

Her paternal great-grandfather, Oscar O’Neill Sr., was president of the Bank of Rio de Janeiro, and when she was an infant the family relocated to the United States, eventually settling in New York, where she grew up in a privileged but emotionally turbulent household.

As a teenager she gravitated to horses and modeling, and by the early 1960s she had been signed to the Ford agency, rapidly becoming a sought-after fashion model whose image appeared frequently in Vogue and Harper’s Bazaar.​

Her modeling success led to a long association with CoverGirl cosmetics, beginning in 1963, and her status as a spokesperson for the brand extended for around three decades, making her one of the company’s most recognizable faces. 

She made her feature-film debut in the comedy “For Love of Ivy” in 1968, and soon afterward won a leading role opposite John Wayne in Howard Hawks’s western “Rio Lobo” (1970), which introduced her to wider cinema audiences. Her breakthrough came with the coming-of-age drama “Summer of ’42” (1971), in which she played a young war bride who becomes the focus of a teenage boy’s romantic fantasies, a performance that turned her into a 1970s screen icon.​

Through the 1970s and early 1980s, she alternated between American and European projects, appearing in Otto Preminger’s “Such Good Friends” (1971), Luchino Visconti’s final film “The Innocent” (1976), and Lucio Fulci’s psychological thriller “The Psychic” (1977).

She later starred in David Cronenberg’s science-fiction horror “Scanners” (1981), further cementing her reputation in genre cinema, and played a leading role in the television adventure series “Cover Up” (1984–1985), which added small-screen visibility to her film and modeling fame.

From the 1990s onward she worked more sporadically, taking parts in independent and faith-oriented productions such as “Doonby” (2013) and the Rachel Scott biographical film “I’m Not Ashamed” (2016), while increasingly shifting her focus to writing and ministry work.​

In 1988 she experienced a religious conversion and became a born-again Christian, a turning point that strongly influenced both her public activism and her subsequent writing. Motivated in part by regret over an abortion she had undergone at age twenty-two, she became active in the anti-abortion movement and emerged as a prominent pro-life speaker and advocate.

She authored several books, including the memoir “Surviving Myself” (1999), in which she recounted her modeling and acting career, multiple marriages and personal crises, struggles with anxiety and postpartum depression, and the development of her Christian faith, along with later works such as the novels “All That Glitters” and “Hillenglade.”​

Alongside her literary and speaking endeavors, Jennifer O’Neill founded Hope & Healing at Hillenglade, an equine-assisted therapy ranch located near Nashville, Tennessee, designed to provide emotional and spiritual support for military veterans and others dealing with trauma and post-traumatic stress disorder.

The program reflects both her lifelong love of horses and her desire to integrate therapeutic horsemanship with Christian counseling, and has hosted thousands of participants in family days, therapeutic sessions, and restorative retreats.

By the 2010s and 2020s, she was widely regarded less as a working actress than as a Brazilian-born American author, activist, and ranch-based ministry leader whose early fame in modeling and film provided the platform for her later humanitarian and religious work.​