Samuel McDonald Martin was born probably in Kilmuir, Trotternish, Isle of Skye, Scotland, some time between 1805 and 1810. He was the son of Mary Nicholson and her husband, John Martin, a doctor. Samuel Martin graduated MD from the University of Glasgow in 1835. It is likely that while in Glasgow he engaged in radical politics connected with the Reform Bill 1832.
Martin emigrated to New South Wales in early 1837, bought land, and engaged in sheepfarming. He visited New Zealand in June 1839, travelling through Northland and the Coromandel Peninsula, where he bought 2,500 acres of land and later jointly owned a sawmill. He was back in Sydney in January 1840 when William Hobson was on his way to take up the lieutenant governorship of New Zealand, and was a member of a deputation to Hobson on New Zealand land claims.
On a second visit, in April 1840, Martin travelled more extensively in New Zealand, met E. J. Wakefield and Te Rauparaha, and spoke with Hobson regarding his land at Coromandel. He received a favourable reply, but the land was ultimately forfeited. Returning to Sydney at the end of 1840, he helped organise a memorial to the British government concerning ownership of land which had been bought from Maori before the proclamation of British sovereignty over New Zealand in 1840. He was appointed a magistrate in New Zealand on 3 May 1841 and reappointed in November 1841.
Martin arrived in Auckland in January 1842 having been appointed editor of the New Zealand Herald and Auckland Gazette on a two year contract and 'a fair salary'. He was disgusted with Willoughby Shortland, the colonial secretary, after Shortland had apparently offered him a bribe to take a pro-government line. Martin began his editorship with an open letter, 'To His Excellency Captain Hobson, R.N.', attacking the New South Wales Land Claims Bill under which pre-1840 land purchases were to be investigated; later editorials criticised government officials, who soon attempted to censor the paper, initially without success. In the controversy Martin resigned his magistracy. When a manuscript was confiscated from the printer, its author, G. B. Earp, a non-official member of the Legislative Council, and Martin, separately challenged the registrar of the Supreme Court to a duel, which he declined. The paper's governmental shareholders suppressed its editorials in early March and closed the paper down on 6 April. Martin brought an action against Shortland and Felton Mathew for the remainder of his two years' salary. At the same time he was sued by Shortland for libel. The jury found for Martin, but the judge, William Martin, awarded him only one year's salary.
With other radicals known as the Senate clique, Martin organised a public meeting at which a memorial to Lord Stanley, secretary of state for the colonies, was drawn up expressing no confidence in Hobson. Soon after Hobson's death, in September 1842, Martin published New Zealand in 1842; or the effects of a bad government on a good country, a pamphlet addressed to Lord Stanley, asking for representative government to be established.
An independent weekly newspaper, the Southern Cross, appeared in April 1843. Martin was editor and his friends William Brown and John Logan Campbell proprietors. Martin continued his trenchant editorials against the government, its extravagant expenditure and corrupt land deals. Brown contributed largely, and Campbell and other Senate members also castigated the inept administration of the acting governor, Willoughby Shortland.
Martin attended the welcome to Governor Robert FitzRoy on 23 December 1843 and was complimented on his paper by FitzRoy, who had read copies of it on his way to New Zealand. Shortland, standing nearby, 'looked like a tiger', and took every compliment to Martin as an insult to himself. FitzRoy appointed Samuel Martin, William Brown and Charles Clifford non-official members of the Legislative Council on 13 May 1844. Martin insisted beforehand on being free to oppose the government both in and outside the Council, but he and his two colleagues were outvoted on most issues. They experienced success, however, in the removal of customs duties.
On 20 December 1844, having resigned from the Council, Martin and Brown left for Britain, intending to petition the House of Commons on behalf of the so-called Senate regarding the treatment of Maori, and colonial trade. During the 5½ month voyage Martin wrote New Zealand in a series of letters (1845), a well-written and wide-ranging account of New Zealand politics since 1839, the country and its climate, colonial and Auckland society, Maori customs and health problems, the New Zealand Company, and many other themes.
Martin returned to Scotland and in July 1847 gave evidence before a select committee of the House of Lords on colonisation from Ireland, drawing on his colonial experiences; his replies were reasoned and succinct. In 1848 he became a magistrate in British Guiana, where his brother, Nicol, was a doctor and a politician. Martin died at Berbice within three months of arrival, on 18 September 1848. It is not known whether he ever married.
Samuel Martin was a well-educated, highly intelligent, egalitarian Scottish Highlander, who had little time for most officials. He deplored the absence of representative government in New Zealand, and criticised Edward Gibbon Wakefield, opposing the immigration of 'paupers' from Britain while there was abundant Maori labour in New Zealand. He was in favour of small landowners from Britain coming to New Zealand and investing their money in the developing colony. He was critical of the Treaty of Waitangi and the apparent bribery used to obtain signatures. While praising New Zealand's climate and agricultural potential, he remarked, 'notwithstanding these advantages, I myself, and nearly every other settler, have been ruined.' He attributed this to the government, which had 'done nothing whatever, either to develop or to make known the natural wealth of New Zealand.' Martin was described by his fellow Scot, John Logan Campbell, as his and William Brown's 'most intimate & only friend…. He is one in a hundred we meet with in these delectable colonies – strictly moral & honest.'