Kinnear studied at Edinburgh Academy before moving to Trinity College, Glenalmond.
He worked as an assistant in an estate in Lanarkshire before he followed his interest in natural history and volunteered at the Royal Scottish Museum with W. Eagle Clarke in 1905–1907.
In 1907, he went aboard a whaling ship around Greenland to collect bird specimens.
He helped the BNHS organize its survey of Indian mammals which were begun around 1911.
When the First World War broke out, he attempted to join the Indian army.