He was a key founder of the Scottish Mountaineering Club and created the eponymous Naismith's rule, used to determine the time necessary to walk a route with a given length and elevation gain.

At an early age, his parents introduced him to mountain climbing in the Scottish Highlands; he climbed Ben Lomond at the age of nine, made a winter ascent of Beinn Bhreac by fourteen and hiked 56 miles (90 km) from his family home in Auchincampbell to the top of Tinto and back.

His difficult ascent of Ben More in 1884 led him to the belief that Scotland's mountains demanded the same level of respect as those in the Alps, and in January 1889 he had a letter published in the Glasgow Herald proposing the formation of a "Scottish Alpine Club".

[1] He is perhaps best known for conceiving Naismith's rule, a method for estimating the amount of time it will take to walk a route according to its distance and elevation gain.

On 27 September 1935, he died suddenly of heart failure at Strathpeffer and was buried on 1 October 1935 at the Bent Cemetery in his hometown of Hamilton.