Bromley-Davenport entered the film business in 1967 as an assistant to Nicholas Ray. Following his apprenticeship, Bromley-Davenport made his directorial debut with the little-seen Whispers of Fear and co-wrote the screenplay for The Haunting of Julia, which was adapted from the Peter Straub novel Julia and starred Mia Farrow in the title role. His biggest commercial success came in the form of Xtro which spawned two sequels related in title only. He made the second installment ' in the USA, and has worked exclusively there ever since. Bromley-Davenport remained within his own low-budget franchise for one more film, and hired Daryl Haney to write the screenplay for '. This began an ongoing professional relationship between himself and Haney that ultimately changed the direction of Bromley-Davenport's career, culminating in a trio of films that are arguably his finest works: Life Among the Cannibals, Erasable You and the true story Mockingbird Don't Sing, starring Sean Young. Three further feature films followed - all of which display his attraction to dark subject matter. His film Smile Pretty follows the true story of a Romanian child, played by teenaged actress Scout Taylor-Compton, who was adopted by an American man with the intention of using her in child pornography in the USA. Haunted Echoes, a ghost story filmed in 2008, reunited him with Sean Young. Frozen Kiss starred Mimi Rogers and was based on the tragic true story of two young people who, after a night of partying and methamphetamine, became disorientated during their drive home in a blizzard and froze to death. The year 2013 marked Bromley-Davenport's first documentary in over 25 years. American Grand captures the work of a team of piano restoration experts as they spend nine months transforming a decaying 1913 Steinway into a revitalized shining beauty. The film was shown on PBS; it was reviewed by Mario Igrec, author of the definitive book on piano rebuilding Pianos Inside Out, as "a brand new piano documentary classic". Christopher O'Riley, host of the National Public Radio program From The Top, wrote that the film displays: "... an unsurpassed confluence of passion and precision in the work of the team in American Grand". From 2016 until its release in 2020, he was occupied with “Mike Garson and his 88 Friends”, a documentary detailing the life and work of pianist, composer and raconteur Mike Garson, perhaps best known for his 20 year collaboration with David Bowie. This film led to further work in the field of classical and jazz films, videos and promotional pieces. Bromley-Davenport has made classical music videos with multiple concert pianists, always displaying a taste for the unusual or outrageous. His 2015 video Yana Reznik plays Rachmaninoff is a costume fantasy set during the First World War. Even though he has made many deviations from the exploitation field since Xtro, the stigma is still attached, as Bromley-Davenport himself admits that: "Getting a start in exploitation films, as I did, suddenly became unfashionable about 20 years ago, and such movies are now regarded as smut, despite the fact that they gave Martin Scorsese, Francis Ford Coppola, Jim Cameron, Joe Dante, Jonathan Demme and countless others their first opportunities to direct a professional movie." In early 2015, Bromley-Davenport announced that Xtro 4 is on the way. A flashback of his Xtro franchise and an Interview was part of the book Adventures In VHS by author Noel Mellor.
