Millar's drafts and preparatory notes for published and unpublished texts and speeches. Also includes conference packs from several events on Van Dyck with annotations, and a notebook on the Lely family written in 1799 by D. Lely.
Millar filed many photographs throughout the research files series (ONM/2 and ONM/3). This series contains a distinct set of photographs of paintings in private collections, largely in the UK, from the 1990s-2000s; and photographs taken at two exhibitions curated by Oliver Millar in the 1970s in London.