Sage’s parentage has not been established, but it is probable that he was a kinsman of Edward Sage, who served as portreeve of the duchy of Cornwall borough of Grampound in 1425-6.
The exact extent of Sage’s landed holdings, which in 1451 were thought to be worth at least £5 p.a., has not been established, but they included property in Grampound held from the Trevelyans, in ‘Tregenseth’, ‘Tregensowyn’ and Sancreed, held from Richard Tredinney†, and probably also in St. Austell.
The pattern of Sage’s subsequent public career suggests how closely he was identified with the court party: even after Suffolk’s disgrace and murder in 1450 he continued to receive periodic appointments to ad hoc commissions in his locality, but he was excluded from such tasks during the periods of the duke of York’s two protectorates. Naturally enough, he came to the fore in the months of the court’s ascendancy after the Yorkist rout at Ludford Bridge in the autumn of 1459. In December of that year he was appointed a commissioner of array in his county, and the following March he was ordered to identify and seize the goods of the duke of York and his south-western supporters who had been attainted by the Coventry Parliament. Simultaneously, he was also given judicial responsibilities to try and punish any who persisted in their allegiance to the Yorkist cause or who had received and harboured such insurgents. The administration set up by the victorious Yorkist lords after the battle of Northampton naturally excluded Sage from similar appointments, but it is a mark of his standing as a professional that he was permitted to remain on the county bench for a few more months. It is possible that when his name was omitted from the first commission of the peace of Edward IV’s reign, he was in fact dead: certainly, he had died by the autumn of 1466, by which time his affairs were being attended to by his executors.
