The foundation stone for Flechtheim’s second career as an art dealer was laid in Paris where he had spend some time in 1906 during his training. It was here that he got to know the colony of German artists at the Café du Dôme and, in 1907, the art dealer Daniel-Henry Kahnweiler (1884–1979) from Mannheim and Pablo Picasso (1881–1973). In just a few years Flechtheim acquired a considerable number of works by the Cubists and was considered one of the greatest collectors of works by Picasso.

In 1909 Flechtheim started to take an active interest in the art scene in Düsseldorf and became involved with the Sonderbund association of artists as its treasurer and a lender of works, and the Berlin Secession. In the ‘key year’ (Florian Illies) Flechtheim opened the ‘gallery for older and modern art’ in Düsseldorf with the support of Paul Cassirer. The elaborately designed catalogue for the opening contains Flechtheim’s enthusiastic and idealistic mission statement: “At last I am now in a position to fulfil a long-cherished wish to involve myself more with all things to do with art. My gallery will help me achieve this.” From this time onwards, Alfred Flechtheim – who had been operating as a marchand amateur without a gallery up until then – was now an art dealer with his own business premises.

The outbreak of World War I in which Flechtheim served as a volunteer interrupted this development and forced him to auction off his collection and the objects in his gallery in 1917. Two years later Flechtheim dared to make a new start on the exclussive Königsallee in Düsseldorf. He complemented his portfolio with artists from France and Germany and brought out exclusive publications parallel to his exhibitions. In 1921 he launched the innovative gallery publication ‘Der Querschnitt’, started establishing branches and representative offices in Berlin, Frankfurt, Cologne and Vienna and engaged Gustav Kahnweiler, Alex Vömel and later Curt Valentin as members of staff. Flechtheim moved to Berlin due to the city’s importance, trusting Alex Vömel to run the gallery in Düsseldorf. Despite the many ups and downs during this period Alfred Flechtheim nevertheless managed to establish his gallery firmly in the contemporary art scene during the 1920s. The vernissages were attended by artists, collectors, the literati, publishers, museum staff and others interested in art. The list of names in the special edition of ‘Der Querschnitt’, published on the occasion of Flechtheim’s 50^th birthday in 1928, which includes Ernest Hemmingway, André Gide, Jean Cocteau and Max Schmeling, is an impressive testimony to the large and international circle of people who had gathered around Flechtheim during this time.

There was strong competition in Berlin thanks to the number of well-heeled collectors living there, with a number of art dealers and galleries in representative locations and with expensively decorated exhibition spaces. Paul Cassirer, who always supported Flechtheim’s business, was a patron to German Impressionist painters as well as artists in Flechtheim’s circle. Heinrich and Justin Thannhauser were based in Berlin from 1927 onwards and covered a very similar spectrum to Flechtheim. Thanks to the experience they had gained over several decades, they profitted from a well structured approach to acquiring new customers and were a serious competitor to Flechtheim’s Berlin gallery. Their counterpart in the Rhineland area were the galleries Abels and that of Johanna Ey which represented the ‘Junges Rheinland’ group of artists whom Flechtheim had publicly provoked back in 1921. Other art galleries in Düsseldorf, such as that run by Max Stern or Georg Paffrath, focused on older works of art and were, as such, not directly in competition.

At the time Black Friday occurred on the New York stock exchange in October 1929, not all loans taken out by the Galerie Flechtheim GmbH had been paid back by any means, sales had declined and the financial situation had became precarious. Flechtheim ultimately felt compelled to terminate annual contracts he had made with artists which provided them with a minimal income. In addition, he could only afford to stage exhibitions when artists were prepared to bear the costs of transporting and insuring the works themselves and printing invitation cards.

In late 1932 and early 1933 Flechtheim held the exhibition ‘Lebendige deutsche Kunst’. As it transpired, this was to be his last show in Germany.