On his arrival, Macartney is said to have spent a short time as a jackaroo before beginning work with the National Australia Bank, working at Maryborough, Ipswich, Normanton and Townsville until 1885. After 1885, Macartney took up work as an articled clerk for solicitors Thynne & Goertz, being admitted as a solicitor in 1891. When Thynne & Goertz was dissolved in 1893, he became Thynne"s business partner and together developed a strong practice, specializing in commercial matters.
Macartney"s first experience in politics was as a wardsman in the Shire of Ithaca from 1899 until 1903 including being its president in 1900.
In that same year, as the Ministerialist candidate, he stood for the state seat of Toowong in a by-election to replace the retiring Thomas Finney. He defeated the Labour candidate, Arthur Lilley, son of the former Queensland Premier, Sir Charles Lilley, by 960 votes to 766.
In 1911, the member for Toowong, Richard Cottell, suddenly died. Macartney resigned as the member for Brisbane North to stand at the upcoming by-election and defeated the Labour candidate, John Gilday, by 2781 votes to 2163 and held the seat for a further nine years until his retirement from politics in 1920.
Macartney was Secretary for Public Lands from 7 February 1911 until 11 December 1912 and was briefly leader of the opposition in 1915 and 1918-1920.
Although a speaker of average ability and overly sensitive to criticism, he chaired several committees and was seen as being politically powerful from 1902 onwards. He argued for one vote one value, took a keen interest in electoral redistributions and in 1905 he was successful in introducing legislation against juvenile smoking. From 1915 until his retirement from parliament, Macartney was at loggerheads with the then Labour Government who saw him as representative of monopolies and the money power.
Premier T. J. Ryan and Macartney had a total dislike of each other with Macartney accusing Ryan of profiting from legal cases while he was attorney-general.
After Macartney resigned from Parliament in 1920 due to health issues, he returned to his legal practice. He also became chairman of directors of Swift Australian Company
Pty Limited and the local board of the National Bank of Australasia Limited. He was also a director of Finney Isles & Company
Limited, Queensland Newspapers Pty Limited and British Traders" Insurance Company
Limited. He was appointed Agent-General for Queensland in London by the Moore Government in 1929, holding the position for two years.
In 1908, Macartney, by now a member of the Opposition, was defeated by Richard Cottell at that year"s snap election. Such was Labor"s disdain for him that in 1916, the Government introduced a constitutional bill designed to disqualify solicitors who acted "for monopoly companies or alien companies" from being members of parliament which became popularly known as the "Thynne and Macartney disabling bill".