He was also appointed to the Order of the Garter, taking the stall vacated by the executed Lord Hastings. This commitment bore further fruit in the autumn of 1483, when a series of plots against the King coalesced into Buckingham's rebellion, a rising in southern and western England under the loose leadership of the Duke of Buckingham. When Richard rose to suppress the rebellion, Stanley and his brother William were at the King's side and were richly rewarded from the forfeited estates of the rebels and Stanley was appointed to Buckingham’s position as Lord High Constable of England. Whilst Stanley might have had no other option than to act as Richard’s loyal subject, it is conceivable that he may himself have become involved in the uprising. His wife, Margaret Beaufort, was a key conspirator, having brokered the marriage alliance between Edward IV’s daughter Elizabeth of York and her son Henry Tudor. Indeed, it was only by giving a solemn undertaking to Richard to keep his wife in custody and to end her intrigues that Stanley saved her from attainder and disgrace and presumably his own position at the same time. Richard was evidently well aware of the threat from this quarter since in the summer of 1485, when Stanley sought permission to leave the court and return to his northern fastness of Lathom, the king insisted that his son, George Stanley, Lord Strange, take his place at court as a token for his father’s good behaviour.
The Stanleys had been communicating with the exiled Henry Tudor for some time and Tudor's strategy of landing in Wales and heading east into central England depended on the acquiescence of Sir William Stanley, as Chamberlain of Chester and north Wales, and by extension on that of Lord Stanley himself. On hearing of the invasion, Richard ordered the two Stanleys to raise the men of the region in readiness to oppose the invader. However, once it was clear that Tudor was marching unopposed through Wales, Richard ordered Lord Stanley to join him without delay. According to the Crowland Chronicle, although Lord Stanley excused himself on the grounds of illness, the 'sweating sickness', by now Richard had firm evidence of the Stanleys’ complicity. After an unsuccessful bid to escape from court, Lord Strange had confessed that he and his uncle, Sir William Stanley, had conspired with Henry Tudor. Richard proclaimed him as traitor, and let it be known that Strange’s life was hostage for his father's loyalty in the coming conflict. Indeed, Richard allegedly issued orders for Strange’s execution on the battlefield, although in the event these were never carried out. Lord Stanley’s response to Richard’s threat was reportedly laconic: “Sire, I have other sons”.
Three armies followed each other into the midlands: Lord Stanley and his forces; then Sir William Stanley; and finally Henry Tudor and a host comprising Tudor retainers, dispossessed Lancastrian exiles and many men of Wales and Cheshire. Lord Stanley may have secretly met with Henry on the eve of the battle, but when the Stanleyites arrived south of the village of Market Bosworth on 22 August they took up a position independent of both the royal forces and the rebel army. In effect, the two brothers played similar roles to those they had played at the Battle of Blore Heath over a quarter of a century earlier. Lord Stanley kept his powder dry, taking no direct part in the action but stood unmoving between the two armies and it was Sir William's decisive intervention that gave Henry the victory. After the despatch of Richard, who had gone into battle crowned, Polydore Vergil records that the fallen coronet was retrieved and placed by Lord Stanley on his stepson’s head before his cheering troops, thereby emphasising the critical role the Stanleys had played in bringing Henry Tudor to the throne.
