Dux Britanniarum was a military post in Roman Britain, probably created by Diocletian or Constantine I during the late third or early fourth century AD.

It is listed in the Notitia Dignitatum as being one of the three commands in Britain, along with the Comes Britanniarum and Count of the Saxon Shore. His troops were limitanei or frontier guards and not the comitatenses or field army commanded by the Comes Britanniarum.

Fourteen units in north Britain listed in the Notitia as being under his command, stationed in either modern Yorkshire, Cumbria or Northumberland. Archaeological evidence indicates there were others that were occupied at the time which are not listed. His forces included three cavalry vexillations with the rest being infantry, overall they were newly-raised units rather than being third century creations. In addition to these fort garrisons, the dux commanded the troops at Hadrian's Wall and the Notitia lists their stations from east to west as well as some further forts on the Cumbrian coast. These troops appear to have been third century regiments although the reliability of the Notitia makes it difficult to infer any solid information from it.