He was a long-standing member of the
Royal Historical Society of Victoria (RHSV). He served as its President (1956–1959) and contributed to its journal,
Victorian Historical Magazine, and to other history and cultural periodicals. He also wrote thirteen entries for the
Australian Dictionary of Biography. He was a prolific bibliographer and produced numerous published bibliographies, including "major contributions to Australian bibliography". His first was
Local Histories of Australia (1954). Others dealt with the
Latrobe Valley,
Burke & Wills,
Australian aviation,
Australian exploration, the
Parliament of Victoria,
Marcus Clarke and
C.J. Dennis. He was appointed the honorary bibliographer at Melbourne University (Baillieu) Library in 1976. He was a contributor to the
Bibliography of Australia (1941–1969). McLaren was a noted book-collector specialising in
Australiana. He was a member of the
Book Collectors Society of Australia and served a term as president of that organisation. He began collecting in 1943 and by 1974 he owned 40,000 books. The book collection grew so large that he had to sell his home in
Malvern and buy a bigger house in the same suburb to accommodate his library. His collection of Australiana books was extensive, "totalling about 35,000 volumes". It was presented to the University of Melbourne where it is housed in the Special Collections (rare books) Department of the
Baillieu Library. A further 5,000 volumes of "local histories, church histories, business histories and organisational histories" were donated to the
National Library of Australia in 1965. ==Other activities==