Louis Hayet had a difficult and itinerant childhood, due to the instability of his father, an amateur artist. He began to draw and produce watercolours from the age of 12. By the age of 20 he produced works with great skill, as demonstrated by his pen drawing Boulevard, Evening, Paris. He made a living in Paris doing various jobs more or less to do with painting. He associated with Camille and Lucien Pissaro, met Seurat and Signac, the poet Paul Fort and Lugné-Poë, founder of the Théâtre de l'Œuvre, for whom he painted several stage sets. He travelled to Algeria.

His rare exhibitions, the last in 1904, met with little response. From 1905 to 1929 he lived in La Frette and continued to travel and paint in Brittany, Rheims and Paris. His artistic activity slowed down after 1929, and he wrote an semi-autobiographical philosophical tale, Kun the Fool (Kun l'Ahuri), and an essay on aesthetics and pictorial method. He fell ill and hardly left his home in Cormeilles-en-Parisis until his death. Jean Sutter, his biographer, estimates Hayet's output at around 400-500 paintings and 300-350 drawings, pastels, watercolours and gouaches. Today his lack of success during his lifetime seems extraordinary. His paintings from 1888 to 1890 are of pure Neo-Impressionist construction, as seen in Place de la Concorde, Grain Market, Café. In 2003 his work featured at the collective thematic exhibition Between Heaven and Earth: Camille Pissarro and the Painters of the Oise Valley (Entre ciel et terre, Camille Pissaro et les peintres de la vallée de l'Oise) at the Musée Tavet-Delacour in Pontoise