Li had graduated from the Central Police College (the forerunner of today's Central Police University) and served a stint as a policeman in Taiwan before enrolling at New York University, where he obtained both Master's and Ph.D. degrees in forensic science. He then became a professor of forensic science at New Haven University in Connecticut.
李昌鈺畢業於我國中央警官學校（警大前身），曾在台灣當過警察，後來在美國紐約大學法庭科學系，順利取得碩博士學位後，便到康乃狄克州的紐海文大學教授刑事鑑識科學。