A Scottish landscape painter, MacWhirter was born in Edinburgh but left soon after he was elected ARSA in 1867 for London. Exhibited at the RA 1865-1904.
At the age of 15 he left his job in a book shop in order to study art at the Trustees Academy, going later with Chalmers, Pettie and others to London. In 1855 he went to visit Austria, Germany, Italy and the Alps. He spend two summers in Norway making detailed sketches of wild flowers. These paintings came to the attention of Ruskin who wrote: 'I have never seen anything like it'. Some of these were subsequently purchased by Ruskin and bequeathed to the Ashmolean Museum.
MacWhirter's preferred subjects were of the peaceful and poetic landscapes, with in particular the high hills and birches of Perthshire. At first he attempted Pre-Raphaelite detail, but later abandoned this for a broader style. He used strong colours and subordinating details to the general effect but in due course he developed a preoccupation with trees, especially the silver birch.