Mowbray was appointed at the Scone parliament of 2 April 1286, together with the bishop of Brechin, the abbot of Jedburgh to seek out King Edward I of England in Gascony and ask for his advice and protection and liberty of Penrith.[1] They were received by Edward I on 15 September 1286 in Saintes, Gascony.[1]
He was one of the sealers of Treaty of Birgham, intended to secure the independence of Scotland after the death of King Alexander III and the accession of his granddaughter Margaret in 1286.[2]
Geoffrey also ratified at the Scottish parliament at Dunferline, the treaty between France and Scotland on 23 February 1296.[3]
He was part of the inner circle of the Balliol administration, during the reign of King John Balliol.[4]
Barrow, Geoffrey Wallis Stewart (October 1990). "Studies Commemorative of the Anniversary of the Death of the Maid of Norway". The Scottish Historical Review. 69 (188 Part 2).
Dowds, T. J. (2014). The origins of Scotland's national identity. Rothersthorpe: T. J. Dowds, Paragon. ISBN978-1-78222-187-6. OCLC876143438.
Young, Alan (1997). Robert the Bruce's rivals: the Comyns, 1212–1314. East Linton, Scotland: Tuckwell Press. ISBN1-86232-053-5. OCLC37976670.