He seems like an incredibly interesting and influential figure of his era, thriving in Revolutionary France as an ultra-leftists, then organising the Thermidorian Reaction. Once that starts going downhill he facilitates Napoleon's rise, where as far as I can tell he becomes some sort of spymaster. And then he finally manages to jump onto the Bourbon Restoration and briefly thrive there. Yet I'm struggling to find English language works on him and his life.
If you can read French, there are two modern biographies of Fouché that examine this figure rather closely. Jean Tulard's Joseph Fouché looks at the police chief's talent for organization and contextualizes his actions within the wider framework of the Enlightenment and Revolution. André Castelot's Fouché, le double jeu is a more popular history biography employs some recent archival findings to shed light on Fouché's memoirs. Neither book has been translated as far as I can ascertain though and the same goes for Louis Madelin's two-volume biography produced at the turn of the century.
There are two, older English-language treatments of Fouché. The first is Stefan Zweig's Joseph Fouché: Portrait of a Politician and Hubert Cole's 1971 book Fouche: The Unprincipled Patriot. There is a recent, self-published book on Fouche, Medusa's Head: The Rise and Survival of Joseph Fouché, Inventor of the Modern Police State, but I am not entirely sure of its quality (self-publication can be a red flag and I could not find any reviews from established site like H-France of the Napoleon-Serie.org). Isser Woloch's Napoleon and his Collaborators does have some bits with Fouché in it, as does Michael Sibelius's various essays on Napoleonic policing. Harold Brown's Ending the French Revolution also has Fouché popping in and out of the attempts to restore order after the Terror.