Angered by Richard of Gloucester’s usurpation of the throne in 1483 and the rumours of the murder of Edward V and his brother in the Tower of London, Edgcumbe joined the rebellion led by Henry Stafford, 2nd Duke of Buckingham to dethrone the Yorkist Richard III and replace him with the Lancastrian Henry Tudor.

[8] He held important offices in the new reign: an MP for Tavistock once again in 1485, Privy Councillor, Comptroller of the Royal Household, Sheriff of Devon in 1487 and Ambassador to Scotland.

He showed his shrewd political judgment in accepting the assurances of loyalty given by Gerald FitzGerald, 8th Earl of Kildare, the most powerful of the Anglo-Irish magnates, whose influence made him an indispensable ally of the Crown; at the same time he showed his independence by refusing, against Kildare's urging, to pardon some of the more notorious rebels, notably Sir James Keating, the Prior of Kilmainham.

He took care to be approachable: having administered the oath of fealty to Thomas Cusack, the Recorder of Dublin, he dined with him "with great cheer".

[10] During his last mission, a diplomatic one to negotiate a truce with Anne, Duchess of Brittany, he died at Morlaix on 8 September 1489 and was buried there.