In 1977, Poonam Dhillon won a beauty pageant that drew attention to her. Legendary filmmaker Yash Chopra then approached Poonam Dhillon in his 1978 film 'Trishul'. The popular song Gapoochi Gapoochi Gum Gum from the film was picturised on her and co-star Sachin Pilgaonkar. She was only 16 at the time.

Poonam Dhillon initially refused Yash Chopra's offer to work in 'Trishul', but the late great producer-director persisted and was eventually able to convince her to be a part of the film under the condition that her filming schedule occurs during her school holidays. 'Trishul' (1978), which also starred Sanjeev Kumar, Amitabh Bachchan, Shashi Kapoor, Rakhee, Hema Malini, and Sachin Pilgaonkar was a blockbuster and Poonam Dhillon went on to star in several successful Bollywood films over the years.