John Longstaff was born in Clunes, Victoria, and from an early age was encouraged by his mother to draw. He commenced studying at the National Gallery of Victoria's school of art in 1882; and, in 1887, was the inaugural recipient of the school's travelling scholarship, enabling him to study at the Académie Cormon in Paris. Spending time with expatriate artist John Peter Russell and also travelling to Spain, his work was exhibited in the Paris Salon. Moving to London in 1893, he gained a reputation as a fashionable portrait painter, though returned to Australia two years later accepting several public commissions. He returned to London in 1901, where he remained until 1920. Longstaff was an established academic realist painter, respected portraitist and exhibited regularly at the Royal Academy.
The outbreak of the First World War affected Longstaff's family, as his three eldest sons had enlisted with the British Army. The impact of this involvement is clear in the emotionally rendered 1916 posthumous painting, Portrait of my son (Lieutenant John Campbell 'Jack' Longstaff). Killed in action on the Somme on 7 July 1916, the young man is in semi-profile. His uniformed figure turns away from the viewer into the dark shadowy background, while his face is bathed in a gentle light. Inscribed verso 'not for public sale', this is a deeply personal image that Longstaff had painted for himself rather than for public exhibition.
As with other Australian artists living in London during the First World War, Longstaff was eager to participate as an artist. With the inception of the Australian official war art scheme in 1917, Longstaff was appointed in May 1918. With the rank of honorary lieutenant, he was attached to the 3rd Australian Division with instructions to complete portraits of military leaders and other significant personnel who, in the opinion of the commanding officers, should be represented. Longstaff also produced studies of military operations and collected data on incidents of the 1918 German spring offensive.
Longstaff worked in France from May to June, and again in September to October 1918. He returned to London in summer and was notified by AIF Headquarters of the arrival of officers on his list. He was still completing portraits in London in 1920. The Memorial commissioned him to paint additional portraits on his return to Australia in 1920 and again in 1923, 1924 and 1928. These formal portraits, painted in subdued tones of brown, khaki with touches of warm light, show Australia's military leaders as strong, noble and capable.
A testament to his popularity as a portrait painter, Longstaff won the Archibald Prize on four occasions. For the remainder of his career he held numerous positions in Australian art societies and organisations. He was also a trustee at the National Gallery of Victoria. Knighted for his services to art in 1933, Sir John Longstaff died in Melbourne on 1 October 1941, aged 79.