Clarence Alphonse Gagnon, RCA was a French Canadian painter, draughtsman, engraver and illustrator, from the province of Quebec. He is well known for his landscape paintings of the Laurentians and the Charlevoix region of eastern Quebec.

Clarence Alphonse Gagnon was born in Montreal, Quebec on November 8, 1881. He was the son of Alphonse E. Gagnon, a milling manager, and a cultured English mother, who was interested in literature. Part of his childhood was spent in Sainte Rose, a village north of Montreal. Early in life, his mother had encouraged him to learn drawing and painting, but his father wanted him to become a businessman.

He studied with William Brymner at the Art Association of Montreal in 1897. Desiring to improve his knowledge about art, he went to the Académie Julian in Paris, and studied with Jean-Paul Laurens from 1904 to 1905. He showed his early promise by winning a bronze medal at the Canadian exhibition at the Louisiana Purchase Exposition in 1904. Before returning to Canada in 1909, Gagnon spent time painting in France and Italy.

He then lived in Baie-Saint-Paul, where he produced many paintings depicting nature and the Canadian people. He invented a new kind of winter landscape that consisted of mountains, valleys, sharp contrasts, vivid colours, and sinuous lines. He became a member of the Royal Canadian Academy of Arts in 1922.

Gagnon took trips to Venice, Rouen, Saint-Malo and the Laurentians in Quebec to paint landscapes. He illustrated the pages of the novel Maria Chapdelaine by Louis Hémon. As well, he was the illustrator for Louis-Frédéric Rouquette in 1929 in Le Grand silence blanc. He lived in France from 1924 to 1936.

In 1919 Gagnon married Lucile Rodier, also a pupil of Brymner. Gagnon advanced modernist painting within Canada. One of his disciples was the painter René Richard. His paintings and etchings are held in many collections across Canada, including the National Gallery of Canada in Ottawa, the Art Gallery of Ontario in Toronto, the McMichael Canadian Art Collection in Kleinburg, Ontario, Montreal Museum of Fine Arts, the Musée National des Beaux-Arts du Québec in Quebec City, the Art Gallery of Alberta in Edmonton, the New Brunswick Museum in Saint John, Art Gallery of Windsor, the Art Gallery of Guelph, and the Vancouver Art Gallery. Gagnon's work is also owned by collections outside Canada, including in England the Victoria and Albert Museum in London, the Walker Art Gallery in Liverpool, and the Manchester Art Gallery , in Argentina at the Fundación Proa in Buenos Aires and in France the Petit Palais in Paris.

Gagnon died on January 5, 1942 at the Royal Victoria Hospital in Montreal. He is buried at the Notre-Dame-des-Neiges Cemetery in Montreal. A bust has been erected in his memory by the Galerie Clarence Gagnon in Quebec City.