[13] During his time as Christchurch city librarian, O'Reilly took two years leave of absence and served as a visiting professor at the Institute of Librarianship at the University of Ibadan in Nigeria.
The following year, O'Reilly helped McCahon secure an exhibition at Helen Hitchings' newly opened dealer gallery in Wellington.
A transformative effect of the exhibition came out of a visit to the library by Eric Westbrook, recently appointed director of Auckland City Art Gallery.
[21] Throughout their long friendship, O'Reilly often accompanied McCahon on his walking field trips taking photographs, looking for subjects, and discussing features of the landscape with the artist.
[22] The art dealer Peter McLeavey recalled of O'Reilly, "He was always taking photographs: he had a sense of history, and the importance of recording the present".
[26] Over the years, McCahon also gifted O'Reilly a number of works including the paintings Crucifixion according to Saint Mark,[27] King of the Jews,[28] and Singing Woman.
O'Reilly went on to become a key figure in an expanding partnership with the artist that eventually changed the gallery dramatically when it became the Govett Art Gallery/Len Lye Centre in 2015.
The first confrontation came the year he arrived when the local fire brigade ordered the removal of Billy Apple's Neon Accumulation on the gallery's back stairs as a hazard.
[40] The following year, attempts to purchase Christine Hellyar's sculpture Country clothesline were equally contentious with a public outcry over its cost and content.
[43] O'Reilly, who had already been involved in a similar refusal by the city council to purchase Colin McCahon's I am Scared, held firm and both items eventually entered the collection.
Described by reviewer and art writer John Daly-Peoples as, ‘a masterpiece of academic scholarship’[48] it publishes letters between the artist Colin McCahon and Ron O’Reilly a long-time collector and supporter between 1944 and 1981.