Douglas began buying and selling books in 1995, while still in high school. He is a member of the major international trade associations, and his business is conducted according to their high ethical standards. For many years Douglas has been a Board member of the Australian and New Zealand Association of Antiquarian Booksellers (ANZAAB); he is also a Mentor for the International League of Antiquarian Booksellers. Douglas works closely with private collectors and public institutions to build their collections, and is a former member of the Collections Management Committee of the State Library of Victoria. Douglas Stewart Fine Books owns a bookshop in High Street, Armadale, Melbourne, open six days a week. Douglas and his team enjoy long term relationships with existing customers, private and institutional, as well as meeting new collectors.
Douglas has served on the Board of ANZAAB most years since 2009, representing the Association at the ILAB Presidents' Meetings in Copenhagen (2017), Tbilisi (2019), by Zoom (2020, 2021), Oxford (2022) and Stockholm (2023). Douglas served as the Vice-President of ANZAAB from 2017 - 2019, and as the President of ANZAAB from 2019 – 2023.
Douglas is also an accredited member of the Australian Antique and Art Dealers Association (AAADA), and the Antiquarian Booksellers Association, U.K. (ABA).