Hoffmann was born in Pirnitz / Brtnice, Moravia (now part of the Czech Republic), Austria-Hungary. He studied at the Higher State Crafts School in Brno / Brünn beginning in 1887 and then worked with the local military planning authority in Würzburg, Germany. Thereafter he studied at the Academy of Fine Arts Vienna with Karl Freiherr von Hasenauer and Otto Wagner, graduating with a Prix de Rome in 1895. In Wagner's office, he met Joseph Maria Olbrich, and together they founded the Vienna Secession in 1897 along with artists Gustav Klimt, and Koloman Moser. Beginning in 1899, he taught at the Kunstgewerbeschule, now University of Applied Arts Vienna. With the Secession, Hoffmann developed strong connections with other artists. He designed installation spaces for Secession exhibitions and a house for Moser which was built from 1901-1903. However, he soon left the Secession in 1905 along with other stylist artists due to conflicts with realist naturalists over differences in artistic vision and disagreement over the premise of Gesamtkunstwerk. With the banker Fritz Wärndorfer and the artist Koloman Moser he established the Wiener Werkstätte, which was to last until 1932. He designed many products for the Wiener Werkstätte of which designer chairs, most notably "Sitzmaschine" Chair, a lamp, and sets of glasses have reached the collection of the Museum of Modern Art, and a tea service has reached the Metropolitan Museum of Art.
Through contacts with Adolphe Stoclet, who sat on the supervisory board of the Austro-Belgischen Eisenbahn-Gesellschaft, the Austrian-Belgian railway company, Hpffmann was commissioned to build the Palais Stoclet in Brussels from 1905 to 1911 for the wealthy banker and railway financier Adolphe Stoclet. This masterpiece of Secession Style, was an example of Gesamtkunstwerk, replete with murals in the dining room by Klimt and four copper figures on the tower by Franz Metzner. In 1907, Hoffmann was co-founder of the Deutscher Werkbund, and in 1912 of the Österreichischer Werkbund. After World War II, he took on official tasks, that of an Austrian general commissioner with the Venice Biennale and a membership in the art senate.
Some of Hoffmann's domestic designs can still be found in production today, such as the Rundes Modell cutlery set that is manufactured by Alessi. Originally produced in silver the range is now produced in high quality stainless steel. Another example of Hoffmann’s strict geometrical lines and the quadratic theme is the iconic Kubus Armchair. Designed in 1910, it was presented at the International Exhibition held in Buenos Aires on the centennial of Argentinean Independence known as May Revolution. Hoffmann's constant use of squares and cubes earned him the nickname Quadratl-Hoffmann ("Square Hoffmann").