The youngest son of Chaïm Eidesas and Brocha Slonimsky from Kaunas, Lithuania, Theo Tobiasse was born in Israel, then a proxy Palestine in 1927, where his parents, of Jewish faith, have lived since 1925, far from the threat of pogroms and political upheavals in Eastern Europe. The family encountered material difficulties and decided to return to Lithuania, to finally leave for Paris in 1931 where his typographer father found work in a Russian printing house.

Théo Tobiasse showed very early dispositions for drawing and painting, and during a visit to the 1937 Universal Exhibition at the Musée D'art Moderne in Paris, he was amazed by Raoul Dufy's La Fée Électricité.

His mother's death in June 1939, followed by the outbreak of the Second World War, the German Occupation, the wearing of the yellow star and his registration at the National Higher School of Decorative Arts refused for racial reasons changed his life. He enrolled in a private advertising drawing class on Boulevard Saint-Michel, which he abandoned nine months later because his family, narrowly escaping the Vélodrome d'Hiver roundup on July 16, 1942, was forced to hide in their apartment in Paris for two years. At the Liberation of Paris, he quickly started a career as an advertising graphic designer at the art printer Draeger, and also made tapestry boxes, theater sets and the windows of Hermès rue du Faubourg Saint-Honoré.

After obtaining French nationality in 1950, a vital need for light, sea and immense sky after the darkness of the dark years of the Nazi Occupation decided them to leave Paris and settle in Nice where he continued his career as a graphic designer, especially at Agence Havas.