Behrens attended the Christianeum Hamburg from September 1877 until Easter 1882. He studied painting in his native Hamburg, as well as in Düsseldorf and Karlsruhe, from 1886 to 1889. In 1890, he married Lilly Kramer and moved to Munich. At first, he worked as a painter, illustrator and bookbinder in an artisanal fashion. He frequented the bohemian circles and was interested in subjects related to the reform of lifestyles. In 1899 Behrens accepted the invitation of the Grand Duke Ernst-Ludwig of Hesse to be the second member of his recently inaugurated Darmstadt Artists’ Colony, where Behrens built his own Jugendstil style house in 1901, and fully conceived everything, from furniture to towels, paintings, pottery, etc. The building of this house is considered to be the turning point in his life, when he left the artistic circles of Munich and showed himself to be a talented architect in his very first project.

In 1903, Behrens was named director of the Kunstgewerbeschule in Düsseldorf, where he implemented successful reforms, developing new ways of teaching design. In 1907, Behrens and ten other people (Hermann Muthesius, Theodor Fischer, Josef Hoffmann, Joseph Maria Olbrich, Bruno Paul, Richard Riemerschmid, Fritz Schumacher, among others), plus twelve companies, gathered to create the German Werkbund. As an organization, it was clearly indebted to the principles and priorities of the Arts and Crafts movement, but tending towards the classical in architecture. Members of the Werkbund were focused on improving the overall level of taste in Germany by improving the design of everyday objects and products. This very practical aspect made it an extremely influential organization among industrialists, public policy experts, designers, investors, critics and academics. His work in the early 1900s included a series of exhibition halls and pavilions, a crematorium and some private houses, which show a new direction immediately after his own Jugendstil house, towards exploring simple, rectilinear volumes and classical sources.

In 1907, AEG (Allgemeine Elektrizitäts-Gesellschaft) retained Behrens as artistic consultant, and his work for AEG was the first large-scale demonstration of the viability and vitality of the Werkbund’s initiatives and objectives. He designed the entire corporate identity (logotype, product design, publicity, etc.) and for that he is considered the first industrial designer in history. He also designed a series of factory buildings for them at their two Berlin factory sites, most famously the 1909 AEG Turbine Factory, at the Moabit site, considered an early example of Modernism. He then went on to design four new buildings at the Humboldthain site, which showed that he was as much interested in massive, bold, classical and picturesque effects depending on the context, as expressing modernity. Since Peter Behrens was a consultant rather than an employee of AEG, he was free to work on other projects, and developed a highly successful architectural practice. In this period his growing office had many students and assistants, some who would go on become leading Modernists, including Ludwig Mies van der Rohe, Le Corbusier, Adolf Meyer, Jean Kramer and Walter Gropius (later to become the first director of the Bauhaus).

In 1922, he accepted an invitation to teach at the Academy of Fine Arts Vienna, becoming head of the architecture school, a post he kept until 1936, whilst also designing for a range of clients across Europe. In 1926, Behrens was commissioned by the Englishman Wenman Joseph Bassett-Lowke to design a family home in Northampton, UK. The house named ‘New Ways’, a stark white walled rectangular volume (with jagged parapets), is often regarded as probably the first modernist house in Britain, and marks Behrens’ turn towards the Modernism of New Objectivity.

In 1925 he was invited by his former student Mies van der Rohe, along with many of the leading German architects working in the new style, to design a residential building in Stuttgart, in the development now known as the Weissenhof. His contribution was a set of apartments in stacked cubic volumes, allowing many apartments to open to large terraces.

In 1928 Behrens won an international competition for the construction of the New Synagogue, in Zilnia, Czechia, which was restored in 2012-17 as a cultural centre. The same year he designed a renovation of the Feller-Stern department store in central Zagreb, Croatia, transforming it from Art Nouveau to a complex almost De Stijl Modernist composition. His 1931 hillside villa for the Clara Gans, daughter of Frankfurt industrialist Adolf Gans, was a similarly complex interplay of rectangular volumes, clad in stone, a fine example of New Objectivity.

In 1929, Behrens was invited to the competition for the design of buildings around a proposed radical redesign of Alexanderplatz in Berlin, and though he came second, his designs for the buildings on the south west side of the new square was preferred by the subsequent developer, and the Alexanderhaus and the Berolinahaus were built by 1932.

In 1929, Behrens, in partnership with former student Alexander Popp, was commissioned to design a new factory for the state-run Austria Tabak in Linz, which was built over a long period, due to the economic conditions, finally completed in 1935. The main building has a very long completely horizontal slightly curved facade, Behrens’ most striking design in the style of New Objectivity.

In 1936 Behrens left Vienna to teach architecture at the Prussian Academy of Arts (now the Akademie der Künste) in Berlin, reportedly with the specific approval of Hitler. Behrens participated in Hitler’s plans for the rebuilding of Berlin with the commission for the new headquarters of the AEG on Albert Speer’s famous planned north–south axis. Speer reported that his selection of Behrens for this commission was rejected by the powerful Alfred Rosenberg, but that his decision was supported by Hitler who admired Behrens’s Saint Petersburg Embassy. Behrens died in the Hotel Bristol in Berlin on 27 February 1940, while seeking refuge there from the cold of his country estate.