[1] He commenced his career as a cadet draftsman in the New South Wales public service.
[3] In this role he designed a range of utilitarian structures such as electricity substations, public toilets and bomb shelters (during World War II).
He also used his town planning skills to improve the Brisbane central business district by removing markets and wharves and introducing parks and gardens.
He tried to introduce a green belt around Brisbane to maintain a separation from its satellite suburbs such as Sandgate, Wynnum, but there was opposition from those who would profit by the sale of the land for houses as well as fears that it would drive up prices within the green belt to unaffordable levels; following a successful legal challenge, the green belt proposal did not proceed.
[1] Between 1952 and 1958, Costello was in a private practice partnership with Harold Cook and Walter Kerrison.