In 1990, having defeated the sitting Liberal member Roger Shipton in a preselection ballot for the Liberal electorate of Higgins, Costello entered the House of Representatives at the age of 32.
In 1990, Costello defeated sitting member Roger Shipton in a preselection ballot for the comfortably safe Liberal electorate of Higgins, the seat once held by Harold Holt. He entered the House of Representatives at the age of 32.