Robert Reinert was born in Vienna, Austria, on April 22, 1872. Nothing is known about his family background and education. Around 1900 he moved to Munich, where he ran the artists' cabaret "Die elf Scharfrichter" (1901-1904) with Frank Wedekind. He wrote a stage play entitled "Die geheimnisvolle Frau" and two novels published in Vienna, "Der Weg zur Sonne" (1906) and "Krieg" (1907).    

His first screenplay was "Der geheimnisvolle Wanderer" (1915, directed by William Wauer), followed by others the same year. He also made his directorial debut later in 1915, with "Küsse, die töten" (1915, co-directed with Leo Peukert).    

Robert Reinert's big breakthrough in the film business came with the scripts for the very successful Homunculus film series (directed by Otto Rippert). The first part, "Homunculus" (1916), was followed in the same year by "Das geheimnisvolle Buch", "Die Liebeskomödie des Homunculus", "Die Vernichtung der Menschheit", "Die Rache des Homunculus" and one year later, 1917, "Das Ende des Homunculus". As film historian Jan-Christopher Horak wrote in a portrait of Reinert, "Reinert’s penchant for 'big themes' and metaphorical content" was already evident here. Horak went on to write, "Six parts of feature film length, Homunculus indicates Reinert’s desire for epic canvases: Homunculus is a synthetic man, created from a test tube, who out of loneliness becomes a cold and heartless manipulator of men. Slipping into the role of both a dictator and a working class political agitator, Homunculus precipitates an all-destructive world war. And yet, he is also a tragic hero, Nietzsche's Superman, who understands that he will for ever be beyond human love, a man without a past or a future."

Reinert subsequently wrote and directed two very successful melodramas, "Der Fluch der Sonne" (1917, based on his novel) and "Der Weg des Todes" (1917). Also in 1917, he became artistic director of the production company Deutsche Bioscope GmbH Berlin. Among his significant works of these years were the lavish "Ahasver" films (1917), a trilogy about the mystical figure of Ahasver, the "Eternal Jew," who roams restlessly through various cities. A contemporary critic judged: "All the merits we pointed out at the time about the powerful film work "Homunculus" also apply to this film."   

In the summer of 1918, Reinert founded his own company in Berlin, Monumental-Filmwerke GmbH. The first Monumental film was "Opium" (1919), a drama set in China, England and India about a British scientist (Eduard von Winterstein) who, after various events and intrigues, himself falls victim to the very drug he is researching. The film was a great success. A critic of the magazine "Der Film" called it "a masterpiece of German cinematography" that "has no need to shy away from foreign competition." A short time later, another review appeared in "Der Film," which stated that the significance of Reinert's work would lie in its innovative aesthetics, among other things, "because photography, with its particular technique, produced images such as had not yet been seen in Germany, and which are likely to be a novelty for foreign countries as well."   

Reinert's next film did not do well at the box office, but it still caused quite a stir: "Nerven" ("Nerves", 1919) is set in Munich shortly after World War I and tells of the dramatic and tragic aftermath of the war through three very different people. Some critics were enthusiastic in their praise for the masterful and beautiful cinematography, for the actors and for the fact that the film felt like something fresh.  

Legend has it that some people who saw the film were admitted to a mental hospital after. However, these are unproven claims. The Süddeutsche Zeitung wrote in 2008: "The images of the troubled times of the Räterepublik seemed all too real to moviegoers (...) The provocative silent film had to endure numerous cuts, re-cuts and in some cases distortions of meaning in the 1920s." (In 2008, the Munich Film Museum presented a carefully reconstructed version).  

In May 1920, Reinert moved the headquarters of Monumental Filmwerke to Munich and merged it with the Münchner Lichtspielkunst AG (MLK, pronounced Emelka). This corporation, founded in 1918 and funded with ten million Reichsmarks, was to be the Bavarian answer to the Prussian Ufa. Reinert was appointed production manager, but gave up the post less than a year later to devote himself to his next major project: The epic two-parter "Sterbende Völker: Heimat in Not" (1922) and "Sterbende Völker: Brennendes Meer" (1922) dealt with the decline of Western civilization, from ancient times to the present. "Sterbende Völker" was a colossal failure, with critics praising its opulent design alone. Reinert's next directorial work, "Die vier letzten Sekunden des Quidam Uhl" (1924), also flopped at the box office.   

When his financially struggling company was liquidated in 1925, Reinert returned to Berlin, where he obtained a position with Ufa. Because of his reputation as an extravagant budget-buster, offers for directing work failed to materialize. Instead, he acted as a writer for other directors' projects. Among others, he wrote the scripts for Nikolai Malikoff's French-German co-production "Die Apachen von Paris" ("Apaches of Paris", 1927) and was part of the writing team for Artur Robison's circus film "Looping the Loop" (1928), which is Reinert's last known work.   

On August 30, 1928, Robert Reinert died in Berlin of a heart attack. He was buried in Munich's Waldfriedhof cemetery.