He served at the Italian Parliament between 1924 and 1926 when he was forced to leave Italy due to the repression of the Fascist government.

[2] He joined the Italian Socialist Party in 1897 and headed its left wing.

[2] He served as the political secretary of the Italian Socialist Party in 1920 replacing Nicola Bombacci in the post.

[6] In the party Gennari was part of the faction led by Antonio Gramsci.

[1] Gennari represented the Italian Communist Party in an international conference organized against war and fascism held in Paris on 23 and 24 November 1935 shortly after the invasion of Abyssinia by the Italian Fascist forces.