During the outbreak of the Wars of Scottish Independence, in 1296, Brougham Castle became an important military base for Robert, and in 1300, King Edward I of England visited there.

In 1308, Robert was granted the remaining moiety of the barony of Appleby, by his childless aunt Idonea de Vipont (d.1333),[3] and thus became one of the most powerful barons in England.

He won great renown at the Siege of Caerlaverock Castle, in 1300, during which his armorials (Chequy or and azure, a fesse gules) were recorded by the heralds on the famous Caerlaverock Roll or Poem, which read (translated from French):[5] "Strength from wisdom drawing, Robert Lord de Clifford's mind is bent on his enemies' subjection.

On 12 March 1308, he was relieved of the marshalcy, the custodianship of Nottingham Castle, and of his Forest justiceship, but on 20 August 1308, he was appointed captain and chief guardian of Scotland.

In 1312, together with Thomas Crouchback, 2nd Earl of Lancaster, he took part in the movement against Piers Gaveston, King Edward II's favourite, whom he besieged at Scarborough Castle.

By Maud, he had four children:[10] Clifford was killed on 24 June 1314 fighting at the Battle of Bannockburn[4] and was buried at Shap Abbey in Westmoreland.