Sir Vernon Haddon Treatt KBE, MM, QC (15 May 1897 – 20 September 1984) was an Australian lawyer, soldier, Rhodes Scholar and politician.

Born in Singleton, New South Wales and educated at Shore School, Treatt interrupted his studies at the University of Sydney to enlist at the outbreak of the First World War.

After briefly practising law in 1923 in Britain, Treatt returned to Australia and was admitted to the New South Wales bar that same year, serving as a Crown Prosecutor at the supreme court.

Treatt entered the New South Wales Legislative Assembly on 26 March 1938, representing the Electoral district of Woollahra for the United Australia Party (UAP).

[3] At Oxford, Treatt gained a Master of Arts and a Bachelor of Civil Law in 1923 and was briefly admitted to the bar at Lincoln's Inn in that year.

When he returned to Australia, Treatt was appointed to the New South Wales Bar and also as the Sub Warden of St Paul's College, University of Sydney from 1925 to 1930.

One of his students was the future Justice of the High Court of Australia, Michael Kirby: "I can still see Mr Vernon Treatt QC coming on to the stage of the Phillip Street Theatre where we took some of our lectures.

I can recall his rasping voice as he intoned the old provisions of section 79, spitting out the exceptionally ugly words of denunciation in the parliamentary prose".

[10] After several years Treatt tried again to enter parliament at the 26 March 1938 state election as the United Australia Party candidate for the seat of Woollahra.

[11] On 16 August 1938, after only serving a few months as a member of parliament, Treatt was appointed as the Minister for Justice in the government of Alexander Mair, who had become Premier after Bertram Stevens was defeated in a motion of no confidence in the house.

It resulted in a Royal Commission in the matter from March to August 1941, chaired by Justice Maxwell, after a censure motion introduced by Labor Leader William McKell was defeated.

[16] Mair resigned in 1944 to be replaced by Reginald Weaver, who then led the hopelessly divided conservative forces to defeat at the 27 May 1944 election, losing another three seats.

At the election on 3 May 1947, Treatt's Liberals and Michael Bruxner's Country Party failed to defeat the Labor government, now under new Premier James McGirr, despite an overall swing of 4.5% and a gain of seven seats.

[20] As opposition leader, Treatt proved effective in attacking the shortcomings of the McGirr's Labor government and in the Labor Party on a national level, particularly in areas of economics: "Because of the inflationary pressure, which is largely a result of the Socialists' own low production policy, continuation of subsidies is necessary on basic everyday goods ..."[21] and utilities: "The public is sick of seeing Ministers hunting up alibis, shifting about from one explanation to another and washing their hands of responsibility for powershortages on some flimsy pretext.

"[22] In matters of ideology, Treatt supported Federal Liberal Leader Robert Menzies in his firm opposition to communism, particularly from the Soviet Union, China and Korea.

Australians must sit up and take just as much notice of what is happening across our narrow northern waters … It is of outstanding importance to Australia that the Western Powers' should secure some uniform policy to combat the Communist Asian menace.

In a speech at Sydney's Lyceum Hall, Treatt warned of Australia's attitudes on its success: "A sort of mental haze seems to obscure the vision splendid that lies before this country.

Cahill had won popular support as a vigorous and impressive minister who had resolved problems with New South Wales' electricity supply and in his first 10 months as premier had reinvigorated the party.

[33] Howarth's resignation split the party and sparked a leadership challenge from Pat Morton, who criticised Treatt's "lack of aggression" towards the Labor government.

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.

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.