Treatt stayed in Parliament until his seat was abolished before the upcoming election in 1962, at which point he stood for the new seat of Bligh. At the 1962 election, Treatt was defeated by the Labor candidate, Tom Morey, gaining only 45.29% of the vote. Treatt then joined local government circles, becoming Chair of the Boundaries Commission from 1964 to 1969 and was later appointed as the Chief Commissioner for the dismissed City of Sydney from 1967 to 1969, overseeing the redistribution of council boundaries and reorganisation of council agencies. He also served as the President of the Sydney Cricket and Sports Ground Trust from 1965 to 1967. For his service as Chief Commissioner, he was knighted as a Knight Commander of the Order of the British Empire (KBE) in 1970.Knight Commander of the Order of the British Empire, KBE, 1 January 1970, itsanhonour.gov.auCitation: Chief Commissioner for Sydney Treatt died on 20 September 1984 in Sydney.
