James Martin was the eldest son of Irish parents. He was born at Middleton, Cork, on 14 May 1820. He arrived in Sydney with his parents in 1821. He was educated at Parramatta and then sent to WT Cape's School and to Sydney College when Cape became its headmaster. He was articled to GR Nichols, the first native-born Australian solicitor, and was himself admitted as a solicitor in May 1845.

By 1839 he was acting editor of the Australian, and had become editor of Lowe's Atlas by 1845. When he won a Legislative Council seat in 1848, an objection, that he lacked the necessary property qualification, was at once raised and sustained. He regained the seat and served on the committee appointed to prepare a draft constitution for the Colony.

He was returned to the Legislative Assembly in the first parliament under Responsible Government and, in the Cowper Ministry, he was made Attorney General. His enemies objected to that appointment because he was not a barrister and, as solicitors then had no right of audience, could not appear in court: a fatal defect in days when the Attorney General personally led in many cases involving the Crown. He was obliged to resign, which in turn contributed to bringing down the government. While the Parker Ministry was in power Martin read for the Bar and secured his admission on 11 September 1857 just in time to become Attorney General in a new ministry under Cowper. By virtue of his office Martin took silk on 12 November 1857. He resigned as Attorney General in 1858, though he retained his parliamentary seat.

On 16 October 1863, he became Premier and Attorney General. His government fell at the polls in 1865. He formed an alliance with Henry Parkes in 1866 that led to his return as Premier and Attorney General until 1868.The alliance failed at length when Parkes withdrew, and Martin resigned soon afterwards. For his public services he was knighted.

Sir Alfred Stephen's dissatisfaction with the Chief Justiceship was an open secret in the 1860s and Martin dearly wanted to succeed him. But, first, the opportunity came in 1870 to form another coalition ministry in which for two years he was again Premier and Attorney General.

He was sworn in as Chief Justice of New South Wales on 19 November 1873. He married Isabella (nee Long) in 1853 and the couple had 15 children. He died an 4 November 1886.

The early career of Sir James Martin as a member of the NSW Legislative Council and later the Legislative Assembly, suffered as a result of his lack of qualifications as a barrister. After his successful admission to the Bar in 1857, Martin was able to fulfil the requirements of the position. Appointed Premier and Attorney-General of New South Wales in 1863, Sir James Martin collaborated with Sir Henry Parkes in a busy program of legislative activity which included the passing of many laws designed to promote social reform. He was renowned as a master of legal principle and court practice. Many of his judgments, particularly those in the area of commercial and common law, command respect today as legal precedents and models of judicial expression.