The newly digitised Manchester Observer (1818–22) was England’s leading radical newspaper at the time of the Peterloo meeting of August 1819, in which it played a central role. For a time it enjoyed the highest circulation of any provincial newspaper, holding a position comparable to that of the Chartist Northern Star twenty years later and pioneering dual publication in Manchester and London. Its columns provide insights into Manchester’s notoriously secretive local government and policing and into the labour and radical movements of its turbulent times. Rich materials in the Home Office papers in the National Archives reveal much about the relationship between radicals in London and in the provinces, and show how local magistrates conspired with government to hound the radical press in the north as prosecutions in London ran into trouble. This article also sheds new light on the founding of the Manchester Guardian, which endured as the Observer’s successor more by avoiding its disasters than by following its example. Despite the imprisonment of four of its main editors and proprietors the Manchester Observer battled on for five years before sinking in calmer water for lack of news.