He painted his last picture in 1962 - The Goldfish Pond at Chartwell - when he was 88. Given by Churchill to his bodyguard Edmund Murray, it sold in 2017 for £357,000 ($705,600).
Another picture of the Chartwell goldfish pond, which had belonged to his daughter Mary Soames, went for a record £1.8 million in 2014.
Now, for the first time, Churchill's articles on art and RA lectures have been gathered together. Historian David Cannadine has edited and introduced them in the book, Churchill: The Statesman as Artist.
"For Churchill, the visual was at least as important as the verbal," says Cannadine.
"While Churchill spent most of his waking hours talking incessantly, preparing and making his speeches, delivering monologues at the lunch and dinner table, and dictating his journalism and his books, painting was the only activity he seems to have carried out in peace and silence.
"It absorbed him for many continuous hours, taking his mind off everything else ..."
Apart from a few drawings done at school and in the Army, Churchill had no interest in art until he visited the National Gallery with his wife, Clementine, in 1915.
"Pausing before the first picture, a very ordinary affair, he appeared absorbed in it," Clementine later said. "For half an hour, he studied its technique minutely. Next day, he again visited the gallery, but I took him in this time by the left entrance instead of the right, so that I might at least be sure that he would not return to the same picture."
At the time, Churchill was in despair after planning the disastrous 1915 Gallipoli campaign and his demotion from his job as First Lord of the Admiralty. He turned to painting as therapy.
"When every fibre of my being was inflamed to action, I was forced to remain a spectator of the tragedy, placed cruelly in a front seat," he said of that moment. "And then it was that the muse of painting came to my rescue."
In the 1920s, he began to write about art for The Strand Magazine, singing the praises of bright colours: "I rejoice with the brilliant ones, and am genuinely sorry for the poor browns."
He adored Turner, the Impressionists and Matisse, particularly their skill in portraying the effect of light on landscape and water.
It was in his Royal Academy dinners that Churchill really enlarged on his feelings about art. In 1927, he addressed the RA banquet on art and politics. "How very lucky artists are ... a class of the most fortunate mortals on the globe," he declared.
"All human beings may be divided exhaustively into two classes - those whose work is their toil and those whose work is their joy. Fancy painting all those delightful scenes and graceful forms, tracing the subtle curves of beauty and marking justly where the flash of light falls among the shadow, and doing all that, not as an amusement, but as a solid profession."
World War II brought an inevitable decline in his art.
Painting with his friend, the artist Paul Maze, in Normandy in summer 1939, he said: "This is the last picture we shall paint in peace for a very long time."
It is striking that, during the war, Britain and Germany were both led by artists.
"Churchill was not a great artist, but he was a very accomplished painter, whereas Hitler had no talent whatsoever," says Cannadine.
Churchill did in fact paint one picture during the war - a view of Marrakesh, in 1943, after meeting Roosevelt in Casablanca. He later gave the picture to Roosevelt.
After losing the 1945 election, Churchill returned to painting in earnest. He told his wife: "This new interest is very necessary in my life."
On his deathbed in 1965, aged 90, immobile and supposedly insensible, his right hand moved in a characteristic way.
He was grasping for a paintbrush, said his daughter Sarah.
