James Alexander Robertson Menzies was born on 21 February 1821 at Mount Alexander (Dunalister), Perthshire, Scotland, son of a local doctor, William Menzies, and his wife, Elizabeth Robertson. Menzies followed his father's profession and, after obtaining a diploma at the Royal College of Surgeons, Edinburgh, in 1840 he practised in his father's district of Loch Rannoch. But in 1853 he decided to emigrate to New Zealand and change his vocation to farming. Menzies married Laetitia Anne Featherston, eldest daughter of Isaac Featherston, provincial superintendent of Wellington, on 3 October 1865. He died on 18 August 1888 at Dunalister, Wyndham, in Southland. His wife survived him by 41 years. They had two sons and three daughters.
Menzies arrived in Wellington in December 1853 on the Despatch, and continued on to Dunedin, arriving in January 1854. There he met Commissioner W. B. D. Mantell, who had negotiated the purchase of Murihiku (the southern part of the South Island) from the Maori and who was about to set off overland to Bluff to make the final payment. Menzies seized the opportunity to travel with Mantell and look for land for a run. Accompanied by three other prospective runholders Menzies explored the Waihopai Plains. His diary records how he camped in a rough shelter on the site of the future Invercargill and shot a wild bull in the surrounding forest. He then continued on to Bluff, where he assisted Mantell in the payout to the Maori. Menzies selected a block of 38,000 acres on the east bank of the Mataura River, near where Wyndham was to be established; he named it Dunalister. When the government resumed the run in 1866, Menzies reduced his holding to 8,000 acres.
Dunalister was away in the hinterland with neither a road nor a railway to the nearest port at Bluff, and like many other early settlers in the south Menzies felt that the Otago Provincial Council was neglecting them in its public works programme. In 1857, as president of the Murihiku Pastoral Association, he mounted a petition for the formation of a new province, to be called Murihiku. He later became the leader of the Southland separatist movement. A public meeting on the separation question was held in Invercargill on 28 March 1860, and Menzies espoused the affirmative while W. F. Tarlton of Invercargill, supported by James Macandrew, the superintendent of Otago, took the negative line. A motion in favour of separation was carried by four votes, and a petition for separation was put in hand. This petition was presented to Parliament and Southland province came into existence on 1 April 1861. After an election in July 1861 Menzies, the obvious choice, was elected superintendent, at the first meeting of the Southland Provincial Council on 3 August 1861.
Under Menzies's guidance the infant province was soon committed to two expensive undertakings, a railway to link the provincial capital, Invercargill, to its port at Bluff, and a wooden railway to Winton in the interior. In proposing the latter Menzies was inspired by the prospect that Invercargill could become the principal supply town for the diggers on the Otago goldfields. Menzies was unlucky: by 1864 the returns from the goldfields were on the decline and settlers were leaving both Otago and Southland in droves.
By the end of 1864 the Southland Provincial Council was £400,000 in debt. Although the council had originally sanctioned the public works proposals and had voted to increase the estimates, it now turned on Menzies. A contemporary said of him that 'he did not understand business'. After an election, in which Menzies topped the poll for Invercargill, the new council at its first meeting on 1 December 1864 rejected his nomination to the superintendency by nine votes to seven. He remained superintendent, however, until 13 January 1865 when the council elected J. P. Taylor as the second superintendent of Southland. Menzies continued to serve on the Southland Provincial Council and later vigorously, but unsuccessfully, opposed the move to reunite with Otago. He lost his fight and the last meeting of the Southland Provincial Council was held on 1 December 1869. Menzies continued to serve the Mataura district on the Otago Provincial Council until it in turn went out of existence. He promoted the interests of Southland in the Legislative Council for 30 years, from 1858 to 1888. There he made one final bid to quash the Otago and Southland Reunion Bill when it was introduced to Parliament in 1870, but the bill was passed on 6 October 1870 and the province of Southland ceased to exist.
Menzies was a tall, commanding figure, who generally wore some distinctive item of Highland garb. A Presbyterian of the old school, he believed in family worship and taught in Sunday schools. A political opponent once said of him, 'No mean action, no dishonest thought could have found harbour in his mental calibre.' As the creator and the first superintendent of Southland he was the most outstanding public figure in the province. In Invercargill, where he later resided, he was either president or a member of almost every public institution including the Caledonian Society, Bluff Harbour Board, Southland Education Board and the Invercargill Savings Bank. Although Menzies did not practise medicine in New Zealand he always responded to a call in an emergency.