Penny was born in London, the daughter of Ray Barnett, a lawyer. She is of Irish, Jewish, and Maltese descent, and has described herself as an "atheist child of a lapsed Jew and a lapsed Catholic". She grew up in Brighton and Lewes, attending the independent school Brighton College with a scholarship. As a teenager she suffered from anorexia and was hospitalised at age 17, subsequently making a recovery.
Penny's blog "Penny Red" was launched in 2007 and was shortlisted for the Orwell Prize for blogging in 2010. She began her career as a staff writer at One in Four magazine and then worked as a reporter and sub-editor for the socialist newspaper Morning Star. She has written columns and features for several publications, and is a columnist and contributing editor for the New Statesman and regular contributor to The Guardian.
In April 2011, Penny presented the Channel 4 Dispatches programme "Cashing In on Degrees", and appeared on the same channel's satirical current affairs programme 10 O'Clock Live and BBC Two's Newsnight.
On 26 March 2012, Penny announced via her Twitter account that she was leaving the New Statesman to take up a full-time post at The Independent newspaper as a reporter and columnist. In October 2012, it was announced that she was leaving The Independent to rejoin the New Statesman (in November) as a columnist and contributing editor.
Penny is the author of Meat Market: Female Flesh Under Capitalism (Zero Books, 2011) and Penny Red: Notes from a New Age of Dissent (Pluto Press, 2011). In Meat Market she criticises liberal feminism as embracing the consumer choice offered by capitalism as the path to female emancipation.Penny Red was shortlisted for the first Bread and Roses Award for Radical Publishing in 2012 after the publication of Discordia: Six Nights in Crisis Athens (Random House, 2012). Her 2013 work Cybersexism: Sex, Gender and Power on the Internet (Bloomsbury, 2013) contemplates online harassment and its motivations.Unspeakable Things: Sex, Lies and Revolution was published in July 2014. Shortly afterwards, Penny stated she had been subjected to "a stream of vile sexist and anti-Semitic abuse" following the book's publication. Everything Belongs to the Future (St. Martins Press-3PL, 2016) followed in 2016. Her seventh book, Bitch Doctrine: Essays for Dissenting Adults, (Bloomsbury Publishing, 2017) was longlisted for the 2018 Orwell Prize.
Penny was selected by Truthdig as "Truthdigger of the Week" for the week of 25 November 2011. In 2012, Tatler magazine described her as one of top 100 'people who matter'. In October 2012, The Daily Telegraph ranked Penny as the 55th most influential left-winger in Britain, reporting that she is "without doubt the loudest and most controversial female voice on the radical left", and the knowledge networking company Editorial Intelligence gave her its "Twitter Public Personality" award. In April 2014, she was announced as an International Nieman Fellow at Harvard University in the United States.
Corbyn, however, has been re-elected by the people of Islington North consistently since 1983 and, like Bernie Sanders in the US, seems as surprised as anyone suddenly to be reaping the rewards of a lifetime of sticking to his principles..."