Innocenti was born into a well-to-do Roman family, the son of an architect, during the period following the Italian unification. His first contact with painting came through a family friend, Ludovico Seitz, who used him as a model for a fresco in the Galleria dei Candelabri in the Vatican when he was 14.

 Innocenti was clear from this time what path his life was to take and with a precocious talent began painting academic canvases under Seitz’s tutelage. His formal artistic training amounted to less than a year at the Institute of Beaux Arts in Rome, which was curtailed when Innocenti became disillusioned with academic teaching. His development after this time owed more to the influence of his contemporaries such as Antonio Mancini, Domenico Morelli and Ettore Tito (with whom he spent the summer of 1898 painting in Venice).

 By the 1890s he was exhibiting in Italy and Germany, and in 1895 illustrated the first of several books for Pirandello (the writer dedicated the Erma Bifronte to him in 1906). A trip to Spain in 1899 left a lasting impression, and by now he was turning to scenes of peasant life with its colorful costumes and local folklore as his principal subject matter. On his return to Rome he became a founder member of the “25 della Campagna Romana”, a group of artists (including Dante Ricci, Enrico Coleman, Umberto Coromaldi and Onorato Carlandi) who would meet to paint and talk in the country outside Rome.

In 1903 he exhibited three works at the Venice Biennale; these exhibits mark a turn in style towards Divisionism, and his subjects foreshadow the anecdotal interior scenes with women at mirrors, at their toilette and reclining in chairs, that characterize his painting in the early years of this century. In 1909 he had an entire room devoted to him at the Biennale and the 20 works he exhibited again shows hazy, bourgeois interiors reminiscent of Boldini and Vuillard, and plein-air landscapes which in some cases verge towards an almost Fauve palette.

In 1912 Innocenti was in the front line in the art movement in Rome and his involvement in the organisation of the Roman Secession led him to Paris with the aim of inviting Rodin to visit the first exhibition, the poster for which had been designed by Balla, in 1913. For the same reason he got in touch with Klimt, whose influence can be detected in the swing towards Art Nouveau in some of Innocenti's work of the period (and also in several works from his later "Egyptian period").

These exhibitions were abruptly broken off by the dramatic onset of World War I, in which Innocenti played a role, but in the immediate postwar years, possibly on account of the political and economic confusion of the moment, he devoted his energy to the cinema, designing costumes and sets for such milestones in movie history as Redemption and Ben Hur.

By 1923 the movie industry was on the verge of collapse and Innocenti paid his first visit to Egypt to organise an exhibition of his work. This experience led him to found Cairo Beaux Arts, whose director he became. The post was to keep him in Egypt for the next fifteen years, an absence from Italy that had the effect of distancing him from developments in the artistic movements of the period, so that by the time he returned to Rome in 1938, he realised that he was totally out of the Italian art world.

In the final years of his life he was awarded the Légion d'Honneur and the Croce di San Maurizio e Lazzaro. A one-man exhibition of his work was held in 1954, and his last public gesture as an artist was the publication of his autobiography, entitled Ricordi d'Arte e di Vita, in 1959.

He died in Rome on 4 July 1961.