Known as Britain's version of Linda Lovelace, she began her career in the 8mm hardcore loops of John Jesnor Lindsay, the first- and most famous- being Miss Bohrloch which won the “Golden Phallus Award” at the Wet Dream Festival held in November 1970 in Amsterdam. Millington starred in around a dozen short hardcore films for John Lindsay, although only four (Miss Bohrloch, Oral Connection, Betrayed and Oh Nurse) have so far resurfaced. These were followed by soft core shorts by Russell Gay (Response,1974) and Harrison Marks (Sex is My Business, circa 1974) and top shelf magazine modeling.

Sex is My Business was shot late on a Saturday night at a sex shop, located on London’s Coventry Street. The storyline concerns a powerful aphrodisiac being dropped by a customer, whose potency renders the shop's staff and customers sex crazy. Millington, dressed in a short see-through dress, is the film's main focus of attention, playing a member of staff who drags a customer into the back room for some multi-position sex, thoughtfully turning on the shop's CCTV camera so others can watch. Sex is My Business was considered something of a ‘lost’ film until a Super 8mm print of the film was located and privately transferred to DVD in 2008. The film subsequently made its internet debut on the 26th July 2008 at the site ZDD Visual Explosion.

Mary Millington committed suicide at age 33, using a deliberate overdose at her home in Walton-on-the-Hill, Surrey. Her life had begun a downward spiral into drug use and depression following continual police raids on her sex shops. She left a suicide note which was found near her body.

She was buried at the St Mary Magdalene Church, Betchetts Green Road in the village of South Holmwood, Surrey. Her grey granite tombstone is situated at the side of the churchyard and bears the surname "Maxted" – her married name. She is buried in the same grave as her mother, Joan Quilter, who died in 1976.