Renau was an important artist during the years of the Spanish Civil War. He was already an established artist when, in 1936, he was given the position of General Director of Arts by the republican government. Renau's task was to safeguard the artistic heritage of Spain during the war. Two years later the government appointed Renau, Director of Graphic Propaganda. He lived up to the title with his steady output of anti-fascist poster art, and is credited with having helped to develop photomontage as an art form.

The above poster is one example of Renau's unusual approach to photomontage. He believed that such works should be done in color, and this philosophy made his work stand out, since all photomontage up until his experiments had been done in black and white. After the fascists succeeded in crushing the Spanish republic Renau went into exile... eventually settling in Mexico, where he worked briefly with the great Mexican muralist Siqueiros. While in Mexico the artist continued to developed photomontage, creating a stunning body of work he called Fata Morgana USA - The American Way of Life. The series, begun in 1940, criticized the consumer culture of the United States, and in many ways it was a forerunner to Pop Art. But Renau's bold, startling, political imagery savaged bourgeois ideology in ways that Pop artists never did.