Jane Coutts was born at Kaiapoi, New Zealand, on 18 May 1858 to Donald Coutts, a farmer, and his wife, Anne Mackay. On 26 December 1879 at Patea she married John Thomson, a civil engineer. They were to have one son. From 1893 to 1909, after spending time in Taranaki, Poverty Bay and Otago, Jane and John Thomson lived at Greymouth, where John worked for the Public Works Department and the Greymouth Harbour Board.
While there Jane began mountaineering. In 1903 she and two others became the first women to cross the Copland Pass, a snow-covered, forested route through the Southern Alps between Mt Cook and south Westland. Their guide, Jack Clarke, needed some persuading to take the women; to make him more amenable one of them, Constance Barnicoat, wore practical men's clothing. Jane seems to have been rather more conservative: although on this occasion she wore knickerbockers and puttees under a long, tight-fitting jacket, on other expeditions she wore a knee-length skirt. Despite their successful crossing, Clarke still declared the route 'unfit for ladies'.
Over the next 12 years Jane did a lot of climbing in the Arthur's Pass district. In 1915, while based for a summer holiday at the Hermitage, Mt Cook, she began a two-year climbing partnership with the Austrian guide Conrad Kain. They ascended many peaks, including Maunga Ma, Mt Jeannette, Malte Brun, and two unnamed peaks. One of these Jane named after her only child, Edgar, who had died after a football accident in 1904. She also climbed a number of peaks without Kain, including Mt Kinsey, Mt Blackburn, The Footstool and Lendenfeld Peak.
On 31 January 1916, after three previous attempts, Thomson and Kain traversed the summits of Mt Cook. Kain was criticised for taking a 57-year-old woman on such a demanding climb without another guide, but it was said that she would have been determined enough to continue alone had he not accompanied her. On the way she acted firmly when Kain was distracted by some young women trampers at Hooker Hut, marching him out by the ear and thrusting his pack at him. Eyeing up a knife-edged ridge at the summit, she was rather appalled, but ignored Kain's concern about deteriorating weather and pressed on. Their decision to traverse the mountain rather than return by the route they had come was an impulsive one, made as they ate tinned pineapple. At one point during their perilous passage off the mountain Kain warned Jane to be careful: 'if you slip here I cannot save you'. He was later to write, 'Mrs Thomson is a skilful climber and knows how to handle the rope at such critical moments'; 'she never played out or showed fear'. Their climb was described as 'a marvellous feat unequalled for daring in the annals of the Southern Alps'. Jane Thomson was the second woman to traverse Mt Cook; the first was Freda Du Faur in 1913.
Jane Thomson lived for her climbing holidays at Mt Cook over these years, as from 1909 she was living in Brooklyn, Wellington, looking after her invalid husband until his death on 11 January 1923. In 1921 she became a member of the New Zealand Alpine Club. In 1927, aged 68, she made the first ascent of the low peak of Mt Rolleston. She moved to Christchurch about 1930. Later, aged 80, she travelled to Kashmir to visit the mountain Nanga Parbat.
Jane Thomson died in Christchurch on 17 July 1944. She had been one of the first to achieve important goals for women mountaineers, and proved that age need be no barrier to participation in the sport.