Robert McNab (1 October 1864 – 3 February 1917) was a New Zealand lawyer, farmer, historian, and politician of the Liberal Party. He was Minister of Justice for the 18 months before his death.
McNab was born in 1864 at Dunragget farm near Invercargill. His parents were Janet and Alexander McNab, a runholder. His father represented the Murihiku electorate on the Otago Provincial Council (1858–1861), and the Cambelltown electorate on the Southland Provincial Council (1861–1865), and was for short periods on the Southland Executive Council and the council's Speaker.
Robert McNab received his education from Invercargill District High School and the University of Otago, from where he graduated with a BA in 1893, an MA in mathematics and mathematical physics in 1885, and LLB in 1891. He was admitted to the bar in 1889 and had a law practice in Invercargill from 1890 to 1896, which was followed by running the family farm on the upper Mataura River.
He represented the Mataura electorate from 1893 to 1896 when he was defeated by George Richardson. In 1898 Richardson was adjudged bankrupt. McNab won the subsequent by-election, and held the seat again to 1908 when he was again defeated, by George James Anderson. In 1914 he won the Hawkes Bay seat, which he held until he died in 1917.
He was a Cabinet Minister, and was Minister of Lands, and Minister of Agriculture, from 1906 to 1908 in the Ward Ministry. He was Minister of Justice, Minister of Marine, and Minister of Stamp Duties from 1915 to his death in 1917 in the Reform Government when Reform was in a temporary wartime coalition with the Liberals.