 In 1981 Howarth joined the New South Wales public service and has held positions with the Department of Industrial Development and Decentralisation, NSW Science and Technology Council, Public Service Board, and the Roads and Traffic Authority.He was appointed director and chief executive of the Royal Botanic Gardens, Sydney in 1996 and as director of the Australian Museum in 2004.On 24 June 1978, Howarth attended the protest that led to the Sydney Mardi Gras and was shocked when "The Sydney Morning Herald" published in full the names of those arrested, leading to many people being outed to their friends and places of employment.