At the party meeting on 6 July, Treatt narrowly defeated Morton with 12 votes to 10. Nevertheless, he did not stay much longer as leader. On 6 August he announced that he would resign four days later:  "Following the unsuccessful challenge for the Parliamentary leadership, it was expected that there would be an end to activities so damaging to the party's morale and effectiveness. Unfortunately these activities have continued. The responsibilities of a political leader, particularly at the present time in New South Wales, are very heavy, and a leader giving of his best is entitled to receive the fullest support from every member of the party. This support has not been forthcoming, and without it the burdens on health and effectiveness would prove too much for any man." The subsequent party meeting produced no obvious candidate for the leadership. Neither Askin nor Morton could obtain a majority of votes. Accordingly, Askin asked another prominent Liberal, Murray Robson, to nominate himself. This solved the problem, and Robson became leader, although Treatt remained in parliament. On 17 June 1955, the Queen granted Treatt permission to retain the title "The Honourable" for life, for having served as Leader of the Opposition and the Executive Council of New South Wales. Robson did not have the chance to lead the Liberals to an election. Morton deposed him in 1955, and proceeded to lead the Coalition to another defeat in March 1956, while Treatt increased his majority within his own electorate (where he remained very popular) to 70.84%. At the next election, in March 1959, Morton and the Coalition lost once more to Cahill, who thereby scored his third consecutive victory. Divorcing his first wife, Treatt remarried to Frankie Jessie Embleton Wilson on 16 May 1960. Frankie Wilson was a lawyer who attended St Mary's Anglican Girls' School in Perth and was the granddaughter of Frank Wilson who twice served as Premier of Western Australia. 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.