Edgar Samuel Paxson was born on April 25, 1852 in East Hamburg, New York to William Hamilton and Christina Humbleton Paxson. At the completion of primary school, his parents sent him to a Quaker boarding school called Friends' Institute. Edgar went to into business with his father painting carriages, lettering, and sign painting.

Edgar married Laura Millicent Johnson at Orchard Park, New York in June 4, 1874. A little over a year later their first child, Loren a son, was born and Paxson left his wife and infant child in New York to head west. Working various jobs, Paxson found himself in Montana where continued to live the life of a frontiersman and served for a time as a scout during the Nez Perce War. Finding steady employment in Deer Lodge, Montana, at his old trade, he sent for his wife and son who joined him in 1879. When work became scarce in Deer Lodge, Paxson accepted a commission in Butte, MT to paint a large mural and moved his family there in 1881 to complete the work. He and Laura had three more children after she joined him in Montana, Lelia, Harry, and Robert.

Paxson joined the Montana National Guard as a private and spent ten years as an active guardsman retiring with the rank of 1st Lieutenant. Paxson became an ardent supporter for war against Spain with the sinking of the USS Maine. He enlisted in April 1898 for two years and mustered into service on May 7 in Helena as 1st Lieutenant, Company G, First Montana Infantry. The Montana guardsmen shipped out for the Philippines on July 18. His son Harry also served as a private in Company G as a musician. Paxson contracted malaria shortly after his arrival in the Philippines and due to the severity of the illness military command released him from active service and shipped him home. Once back in Butte, he received his honorable discharge from the Montana Volunteer Infantry on December 2, 1898. While he convalesced, Edgar began working on his Custer painting, completing his canvas titled Custer's Last Battle on the Little Big Horn in 1899. He and Laura also waited and worried about their son Harry. Although the war with Spain had all but concluded in the Philippines by the time the 1st Montana Volunteers arrived war broke out in early 1899 between the Filipino Insurgents and the U.S. liberates delaying the return of the Montanans. During the fighting Harry Paxson served as bugler and courier for General George Crook. Meanwhile, in anticipation of the return of the 1st Montana Volunteers, the city of Butte commissioned Paxson to design a large triumphal arch and sculpt a statue called Peace for the top to welcome and commemorate their return in October 1899.

Paxson's fulltime painting career began with his return from the Spanish-American War with exhibitions in Chicago, the Louisiana Purchase Exposition in St. Louis (1904), as well as the Lewis and Clark Exposition in Portland, Oregon (1905). That same year the Montana State Legislature passed a "resolution of appreciation" in recognition of his exhibit in Portland. The family moved to Missoula in 1906 where Paxson built a studio next to their residence. Six years later the Missoula County Commissioners engaged Paxson to paint eight murals for the county courthouse—Arrival of Father Ravalli at Fort Owen, Lewis and Clark's Camp at Lolo Creek, A Montana Roundup, The Flatheads in Buffalo Country, Lewis' Party Crossing the Clark Fork, Flatheads Leaving Their Bitterroot Home, Governor Steven's Treaty with the Pend D'Oreilles, Flatheads, and Kootenai at Council Grove, and Early Transportation.

With the expansion of the Montana capital in 1912, Paxson, Charles M. Russell, and R.E. DeCamp, all Montana artists, received commissions to produce murals for the new wings based on subjects selected by Governor Joseph K. Toole. Paxson, responsible for the murals in the House of Representatives, painted the six murals that hang in the lobby today: After the Whiteman's Book, The Border Land, Lewis at Black Eagle Falls, Pierre de La Verendrye, Lewis and Clark at Three Forks, and Surrender of Chief Joseph.

The popularity he enjoyed as an artist peaked 1900-1915, after that period he did not receive any more major commissions and as his popularity waned his health also began to fail. Further complicating his health was the unexpected death of his son Harry in January 1910. Electrocuted while working on a dredge near Butte, twenty-nine-year-old Harry left behind a wife and two young sons. Despite his declining health and personal tragedy, Paxson experienced a high point in his career during this time and sales of his painting remained strong although he received little publicity outside of Montana. After 1915 his popularity as an artist began to subside and major commissions and sales dried up but Paxson remained dedicated to his art and even as his health declined he continued to paint.

Contemporary newspaper accounts attributed his health issues with an accident that occurred during his return voyage from the Philippines when the ship he was on encountered a typhoon. Struck by a wave in the storm and thrown against a spar, Paxson suffered an internal injury that plagued him for the remainder of his life. This didn't keep him for volunteering for military service when the United State declared war in April 1917 against Germany but his days of active service were over.

Edgar S. Paxson died November 9, 1919 at the age of 67 at his home in Missoula. His friend Charlie Russell wrote "his work tells me that he loved the Old West, and those who loved her I count as friends." His wife Laura died almost twenty years to the day. They are both interred at the Missoula Cemetery.