Munnings was born in Mendham, Suffolk, England, on 8 October, 1878. At the age of 14 he was apprenticed to Page Brothers & Company, a Norfolk lithography firm; he studied during the evenings at the Norwich School of Art. He had exhibited his work at both the Royal Institute of Watercolour Artists and the Royal Academy by the age of 21; in 1899 he sold Pike Fishing in January, which he had painted three years before, from the Royal Academy exhibition and went to the races to celebrate. The racing world, both on the track and off, inspired him, and in the following years he established himself as a painter of horses and related subjects. An accident deprived him of the use of one eye when he was in his early twenties, but he persevered; his work, including such subjects as flat racing, steeplechasing, foxhunting and Gypsies on the moors, met with critical acclaim.

He made his living painting commissioned portraits of horses--hunters with their owners, racehorses with their jockeys and the like; he was considered second only to George Stubbs among British painters of horses. He was created a Knight Commander of the Victorian Order in 1944. He also served as President of the Royal Academy from 1944 to 1949; he resigned after his strong dislike for modern art and his utter lack of patience with those who did not agree with him on this point made his position untenable. He continued to paint, although toward the end of his life his gout, which he had contracted at the age of 30, was so painful that he was unable to hold a brush. He also wrote a three-volume autobiography, consisting of An Artist's Life, The Second Burst, and The Finish. He exhibited regularly at the Royal Academy before, during and after his presidency, showing a total of 290 paintings there during his work and six more the year after his death.

Munnings died in Dedham, Essex, England, on 17 July, 1959.