Mägi received his elementary art education in 1899–1902 from the drawing courses of the German Artisans' Society of Tartu. At the same time, he was keenly engaged in theater, violin play and different sports.
He continued his art education in 1903–1905 as am unattached student in Saint Petersburg. In the autumn of 1907 he went to Paris. There he studied at a free academy. In 1908–1910 he lived in Norway.
In 1912, he returned to Tartusse. He worked there as an art teacher.
Konrad Mägi was one of the most colour sensitive Estonian painters of the first decades of the 20th century.
In Åland, he made delicate plant vignettes in the style of Art Nouveau: Kahekesi (Two together; 1908; China ink drawing).
In Paris, he had contacts with Impressionism and Fauvism. These influences changed his colours: Lilleline väli majakesega (A flower field with a little house; 1908–1909), Norra maastik männiga (A Norwegian landscape with a pine; 1910).
Mägi's works on motives of the island of Saaremaa are the first modern Estonian nature paintings.
From 1918, influence of Expressionism is manifest, fostered by Mägi's extreme sensitivity and emotional response to the anxious times: Pühajärv (Lake of Pühajärv; 1918–1920), Otepää maastik (Landscape of Otepää; 1918–1920). Also influenced by Expressionism are his big figure compositions Pietà (1919), Kolgata (Golgatha; 1921).
His new artistic period, started by a trip to Italy, brought calmer tempers: Varemed Capril (Ruins in Capri; 1922–1923).
Along with nature pictures, he painted flowers and portraits. His mostly beautiful female models express the Art Nouveau ideal of beauty: Holsti (1916).
In his later portraits from the 1920s, a more serious temper is expressed: Madonna (1923–1924).