Henderson was a socialist, and beside his academic work for the University, he produced translations of the Prison Letters of Antonio Gramsci, whom he had first heard of among Communist Italian partisans during the war. The translation was published in the "New Edinburgh Review" in 1974 and as a book in 1988. He was involved in campaigns for Scottish home rule and in the foundation of the 1970s Scottish Labour Party. Henderson, who was openly bisexual, was vocal about gay rights and acceptance.