Sir Josiah Henry Symon KCMG KC (27 September 1846 – 29 March 1934) was an Australian lawyer and politician. He was a Senator for South Australia from 1901 to 1913 and Attorney-General of Australia from 1904 to 1905.

Symon was born in Wick, Caithness, Scotland. He immigrated to South Australia in 1866 and became one of the colony's leading barristers. He was appointed Attorney-General of South Australia in 1881, serving only a few months, and won election to the Parliament of South Australia in the same year. Symon supported the federation movement and won election to the Senate at the 1901 federal election. He served as Attorney-General in the Reid government (1904–1905). After his death he donated his extensive personal collection to the State Library of South Australia.

Symon was born in Wick, a town in the county of Caithness in the Scottish Highlands, in 1846. He was educated at Stirling High School, where he was the dux in 1862, before attending the Free Church Training College in Edinburgh. His brother, David Symon, was a member of the Legislative Assembly of Western Australia. He was a distant cousin of Magnus Cormack, who was also born in Wick and served as President of the Senate in the 1970s.

In 1866 he emigrated to South Australia and was employed as an articled clerk with his cousin, J. D. Sutherland, a solicitor in the city of Mount Gambier. The leader of the South Australian Bar Association at the time (and a future Chief Justice of South Australia), Samuel Way, noticed Symon's work and invited him to join his firm. Symon, having completed his studies, was called to the bar in 1871, and admitted to practice as a barrister. In 1872, after the death of one of the partners at Way's firm, Symon became a partner alongside Way. In 1876, Way was appointed as a judge, and Symon bought out his part of the business.

In March 1881, Symon was made Attorney-General of South Australia in the Morgan government, although at the time he had not been elected to the Parliament of South Australia. He was elected as the member for Sturt in the South Australian House of Assembly several weeks later. However, the Morgan government lost power on 24 June of that year, and Symon lost his position as Attorney-General. Later in 1881, Symon was made a Queen's Counsel, and on 8 December of that year he married Mary Cowle, with whom he was to have five sons and seven daughters. In 1884, Symon was offered a judicial position, but he declined to accept it. He travelled to England in 1886, and was offered a nomination for a seat in the British House of Commons, however he declined this opportunity also. In 1887, after returning to Australia, he lost his seat in the South Australian parliament.

He was a highly effective and ruthless advocate: in 1889 he successfully prosecuted the William Hutchison libel case against J. B. Mather and George Ash of The Narracoorte Herald. In his highly technical argument he succeeded in having evidence from Hansard and Crown Law documents ruled as inadmissible. Ash (who conducted his own defence) then turned to politics and law, and after his untimely death received glowing tributes from Symon.

Symon was an ardent supporter of the cause of Federation, and frustrated by the apathy the question commonly received in South Australia. He successfully stood as a candidate for the Australasian Federal Convention of 1897-8, and was on the side of the majority in 71 percent of its divisions; a higher percentage than the great bulk of delegates. In the subsequent struggle to win the support of the electorate for the proposed federal constitution, he was a significant behind the scenes player, sought out by Alfred Deakin, for example, to arrange funding for Federationist candidates in the NSW general election of 1898. Symon was knighted on the day of the proclamation of the new Commonwealth.

Symon stood for election to the Australian Senate at the 1901 election for the Free Trade Party, and was placed first overall by the voters of South Australia. He was made leader of the opposition in the Senate, and was a leader within the Free Trade Party on tariff policy. After being elected to the Parliament, he stood down from his position as a member of the council of the University of Adelaide, a position he had held since 1897. In 1902, he was involved as the defense council in the highly publicised murder of Bertha Schippan trial. At the 1903 election he again topped the poll for the Senate in South Australia. When the High Court of Australia was created in late 1903, Symon was mentioned in the press as a possible judge of the court, although ultimately he was not appointed. From August 1904 to July 1905 he was the Attorney-General of Australia in the Reid Ministry.