Lithostratigraphical and biostratigraphical revisions are reported within the classic Windermere Supergroup succession of the southern Howgill Fells of Cumbria, and a review is provided of the depositional environment of this Late Ordovician and Silurian foreland basin sequence. In particular, a number of key marker beds are described and better located, both geographically and stratigraphically. These markers include: (a) a unit of conglomerate and sandstone, probably syn-glacial, in the upper (Ashgill) part of the Dent Group; (b) the basal, carbonate, Spengill Member (uppermost Ashgill) of the Stockdale Group; (c) the ‘Green Streak’ oxic mudstone higher in the Skelgill Formation (Llandovery) of the same group; (d) the ‘Red Beds’ – newly defined as the Hebblethwaite Member – in the Browgill Formation of the Stockdale Group; and (e) the oxic Coldwell Formation within the predominantly anoxic Tranearth Group (Wenlock). The thick, turbiditic Coniston Group is divided using thin-bedded units rich in anoxic hemipelagic mudstone, and its biostratigraphical zonation and transition into the Bannisdale Formation is better defined. The graptolite Saetograptus soperi sp. nov. is described, and shown to characterize a new biozone below the leintwardinensis Biozone. The revised division of the Coniston Group allows a new correlation of the group across NW England, defining turbidite system architectures that imply control of sedimentation by syndepositional faults.