From its inception, McDiarmid's art career encompassed, as both subject and inspiration, gay male sexuality, politics and urban subcultures.
His creative techniques included: collage, painting, drawing, calligraphy, mosaic, installation, various forms of print-making, sculpture and artist's books.
The following year, McDiarmid visited the United States, where he travelled extensively on the east and west coasts between March and October; in particular the gay communities of the Castro in San Francisco and Christopher Street area in Lower Manhattan, New York.
Later in 1978, McDiarmid and Peter Tully jointly created the installation 'The Strine Shrine' at Hogarth Galleries, again referencing the icons of Australian suburbia.
[13] The move to New York coincided with the establishment of the black and Hispanic, gay underground dance club Paradise Garage, of which McDiarmid was an early devotee.
[14] Paradise Garage served as an inspiration for a suite of work to which McDiarmid gave the title "Disco Kwilts", produced between 1979 and 1981, using newly available material: holographic reflective Mylar sheeting.
[16] One of the first Sydney exhibitions that McDiarmid was involved with following his move to New York was the 'Project 33: Art Clothes' exhibition at the Art Gallery of New South Wales (AGNSW) (1980–1981), curated by Jane de Teliga, which also included works by Linda Jackson, Jenny Kee, Peter Tully, Jenny Bannister, Katie Pye, Bruce Goold and others.
In 1983–84, he produced a series of acrylic paintings on cotton with entwined calligraphy and decorative graphic forms conveying the excitement, exploitation and joy of life in the city: sex, gay rights, cruising, romantic love and the emergence of HIV/AIDS.
His influential one-person exhibition focussing on the sexual and cultural politics of AIDS, 'Kiss of Light', was held at the Syme Dodson Gallery, Sydney in 1991.
[20] He was recognised in this period for his support of lesbian contributions to the culture and design aesthetic of the Mardi Gras parade, party and festival.
The graphics from his 1992 Safe Sex posters which were also subsequently enlarged to form gigantic moving figures for the Mardi Gras parade.
[22] This was presented at the Melbourne conference ‘AIDS: Towards a Paradigm’ (and later developed into the digital film "A Short History of Facial Hair" for a London exhibition in 2011).
He became an advocate for effective estate planning for artists, spoke at Sydney Writers Festival on the subject in 1994 and made speaking appearances in association with the Arts Law Centre of Australia.
This musical movement was performed at the McDiarmid retrospective at the National Gallery of Victoria in July 2014, preceded by a forty-minute conversation between the composer and the former Judge of the High Court of Australia the Hon.