Assembly seat of Sturt as a National Party candidate, and on 6 April he was elected first of the three with 19.2 per cent of the vote. As a parliamentarian, Blackburn's speeches were generally about issues affecting those still serving overseas, as well as returned soldiers. A notable exception was his successful motion in favour of a profit-sharing system for industrial employees. He advocated several radical ideas in his time as a parliamentarian, including removing all single men from the state public service so they would be free to enlist. He was also criticised in Parliament for not paying due attention to important legislation regarding ex-soldiers. This criticism even extended to attacks from another AIF man, Bill Denny, from the opposition Australian Labor Party (ALP). According to his biographer Andrew Faulkner, his time in Parliament showed Blackburn to be a man of few words, but his words were chosen well and delivered with authority. On 29 August 1918, he was appointed a justice of the peace, and in November, he became a Freemason with the St Peter's Collegiate Lodge. In July 1919, the Returned Sailors' and Soldiers' Imperial League of Australia (RSSILA), which had succeeded the RSA, held its annual congress in Adelaide. Among the motions that Blackburn moved was one calling on the federal government to ensure that a suitable headstone was erected over the grave of every sailor and soldier killed during the war. He also railed against delays in the deferred pay of dead soldiers being paid to their widows. In January 1920, Blackburn was re-elected as state president of the RSSILA, although this was the first time he was opposed for the post, and he only won narrowly. By this time he had built the state branch of the organisation to 17,000 members. During that year, he hosted visits by two notables; Field Marshal William Birdwood, and the Prince of Wales, who later became King Edward VIII. In accordance with normal procedures, while serving in the AIF, Blackburn had been appointed an honorary lieutenant in the CMF on 20 February 1916 on the Reserve of Officers List. This appointment was made substantive on 1 October 1920, still on the Reserve of Officers List. Continuing to practise law while a member of Parliament made for a heavy workload, and Blackburn did not seek re-election in 1921. In the same year he relinquished his role as state president