Roger was the son of Godfrey de Mowbray and a daughter of John Comyn, Lord of Badenoch and Alice de Ros.
He held the office of Standard Bearer of Scotland and signed the Declaration of Arbroath in 1320 and then was arrested later in 1320 for treason for plotting to overthrow King Robert I. He died of wounds suffered during his arrest. Roger's corpse was brought to Parliament in a litter and was found guilty and sentenced to be drawn, hung and beheaded. King Robert I gave clemency and his body was allowed to be buried. His lands of Barnbougle and Dalmeny, Inverkeithing, Cessford and Eckford, Methven, Kellie and Kirk Michael were forfeited to the Crown.