Siddiqui is credited for pioneering the isolation of unique chemical compounds from the Neem ("Azadirachta indica"), Rauvolfia, and various other flora. As the founder director of H.E.J. Research Institute of Chemistry, he revolutionised research of the pharmacology of various domestic plants found in South Asia to extract novel chemical substances of medicinal importance. During his career, Siddiqui published more than 300 research papers and obtained 40 patents mainly from the field of natural product chemistry. In addition to his scientific talents, Siddiqui was also an avid painter, poet, and a great connoisseur of Western music. His paintings were exhibited in the United States, Germany, India, and Pakistan.