As a student activist and member of the Trotskyist group, the International Socialist Organisation (ISO), Sparrow was one of the Austudy Five, controversially arrested after a protest in 1992. He was expelled from the ISO in 1995 and helped found the splinter organisation, Socialist Alternative (SA). After leaving SA, he was involved for some years in the group Civil Rights Defence.

Radical Melbourne presents a guide through the first hundred years of political radicalism in Melbourne, focusing on the structures, streets and public places that remain today, and illustrated by rarely-seen images from the archives of the State Library of Victoria. Controversial journalist and author John Pilger called Radical Melbourne "a brilliantly original, long overdue unveiling of a great city's true past". The book inspired Radical Brisbane, a similar project about the Queensland capital, by Raymond Evans and Carole Ferrier.

The sequel, Radical Melbourne 2: The enemy within, was described by reviewer Ian Morrison as "sparkl[ing] with furious wit ... the Sparrows are devastatingly funny."

Communism: A Love Story is a biography of the radical intellectual Guido Baracchi, a founder of the Communist Party of Australia. The book traces Baracchi's political career from his support for the Industrial Workers of the World to his association with the Trotskyist Fourth International; it also examines his turbulent personal life and his relationships with writers such as Katharine Susannah Prichard, Lesbia Harford and Betty Roland. It was shortlisted for the Colin Roderick Award.

Killing: Misadventures in Violence is a study of the social and psychological consequences of executions, combat and animal slaughter. It was a finalist in the Melbourne Prize for Literature Best Writing Award 2009.

After completing a PhD in Creative Media at RMIT University in 2007, Sparrow became a Research Fellow at Victoria University and the editor of the literary journal Overland. His work has appeared in The Age, The Sydney Morning Herald, Overland, Arena, Meanjin and other print publications; he contributes regularly to Crikey, New Matilda, ABC The Drum Unleashed and other online outlets.In late 2009, he began co-hosting the Aural Text show on Melbourne radio station 3RRR with Alicia Sometimes.