Barnett was a student at Cambridge University, where he was active in the Labour Club,and lodged with Nicholas Kaldor.

[2][3] He was a Fellow of the Transnational Institute from 1974 to 1984 and remains a contributor[4] Barnett has written for the New Statesman,[5] The Guardian,[6][7] Prospect.

He conceived the television film England's Henry Moore (1988), which concerned the sculptor's co-option by the British establishment.

[11] Barnett founded openDemocracy, launched in 2001, with Paul Hilder, Susie Richards and David Hayes, and was its Editor and then its first Editor-in-Chief until 2007.

[12] Barnett is the author of several books, including Iron Britannia, Why Parliament Waged its Falklands War (first published by Allison & Busby in 1982, reissued by Faber Finds in 2012.

His in-depth evaluation was published by Unbound in 2017 with the title The Lure of Greatness: England's Brexit and America's Trump.

[16]Barnett made a short film in 2022 on American politics: US Progressives on a Knife Edge[17] and in August 2024 he wrote an article about the dangers of surveillance in The Washington Spectator entitled Switch It Off!.