Almost a year earlier, in July 1469, an army loyal to the Yorkist king, King Edward IV was defeated at the Battle of Edgecote Moor by Richard Neville, 16th Earl of Warwick, his disaffected former supporter; Edward himself was subsequently captured in Olney, Buckinghamshire. However, with the help and support of his brother Richard, Duke of Gloucester, he had by now regained power. Despite the nominal reconciliation of Warwick and the king, by March 1470 Warwick found himself in a similar position to that which he had been in before the battle of Edgecote. He was unable to exercise any control over, or influence, Edward's policies. Warwick wanted to place another of the King's brothers, George, Duke of Clarence, on the throne so that he could regain his influence. To do so, he called on former supporters of the defeated House of Lancaster.
The rebellion was initiated in 1470 by Sir Robert Welles, son of Richard Welles, 7th Baron Welles, a former Lancastrian, when his family fell foul of Edward. Sir Robert turned to Warwick for help. Warwick judged the time was ripe for another coup d'état, to kill Edward or remove him from the throne.
Welles started gathering troops at his base in Lincolnshire, ready for a show of arms against the King. The unrest in Lincolnshire prompted the King to act, and he started gathering men for his army on 4 March. The news of the King's intention to march to Lincolnshire quickly spread panic among people there. Due to Welles' deliberate misinterpretation, rumours were quickly spread that the King was coming to try the previously pardoned rebels from Edgecote, and that he would "hang and draw a great number" of them.
With the encouragement of Warwick and Clarence, Welles set himself up as a "great captain" of the people of Lincolnshire. On 4 March summons were sent to all the surrounding estates requesting every able man to join him in resisting the King. On the 7th the King heard that the rebels were marching towards Stamford with an army of 100,000 men, having recruited many men from nearby counties, especially from Yorkshire.
The King later received letters from Clarence and Warwick stating they were marching North with all their men to support the King. The King then unsuspectingly issued commissions of array which included Warwick's name, authorising him to raise his own army of professional soldiers. Edward then received news that the rebels had changed course for Leicester, as had Warwick and Clarence, which revealed their intentions.
Welles received a letter from the King telling him to disband his rebel army, or his father Lord Welles (previously taken prisoner by Edward) would be executed. Welles quickly turned back with his army to Stamford. Edward's confidence grew when Welles failed to rendezvous with Warwick and his experienced forces.