Undeterred by the defeat at Mortimer's Cross, Margaret of Anjou marched her troops south to regain control of the capital and the king. On January 20 she reached York, where her troops met up with the main Lancastrian army. As this army moved south, it was also joined by some of the Welsh soldiers escaping from Mortimer’s Cross. The Lancastrian army was captained by Somerset, Exeter, Devon, Shrewsbury, Nothumberland, Clifford, Grey, Roos and Trollope. The Lancastrians, who numbered more than 25,000, had by far the greater number of nobles in their ranks.

The Yorkists continued with their propaganda campaign in the south, and the behavior of the Lancastrian army fed into it. Many towns, particularly those with Yorkist sympathies, suffered a great deal of damage from the Lancastrians as they passed through on their way south. Panic set in in London, and citizens began to board up their homes and bury their possessions. Great numbers of armed men began arriving in London voluntarily, offering to join the Earl of Warwick, the man they believed would save the south from the northern hordes.

On February 12 Warwick marched out of London, with an army numbering about twenty-five thousand men. He took Henry VI with him under guard. In Warwick’s army were his brother John, recently created Lord Montagu, John Mowbray, the Duke of Norfolk, William Fitzalan, the Earl of Suffolk and John de la Pole, the Earl of Arundel. He was also accompanied by Lords Fauconberg, Bonville and Berners, and his loyal retainer, Sir John Wenlock. The Duke of Burgundy also provided a contingent of handgunners to the Yorkist cause. The left flank was under the command of Montagu, the right under Norfolk and the center under Warwick himself.

The Yorkists arrived in St Albans the following day, and Warwick spent the next few days reinforcing the Yorkist position. Early in the morning of February 17 the Lancastrians entered the town from the northwest, meeting with the Yorkists in the market square, but were pushed back by Warwick’s archers. Despite heavy casualties the Lancastrians forced the Yorkists out of the town to Bernard's Heath. Warwick succeeded in regrouping his men, and it was here that the fiercest fighting of the day ensued. The Yorkist cannon were almost useless, as snow had started to fall, dampening the powder. Some of the handguns backfired, causing dreadful injuries to their owners.

The fighting continued until dusk but the Lancastrians were eventually able to break through the Yorkist lines. Warwick sounded the retreat and withdrew some of his troops into a defensive position to the north of St Albans. The Yorkists withdrew from St Albans that night with a force of 4,000 men, and hoped to link up with Edward at York.

The battle was a significant victory for the Lancastrians, in fact their most decisive victory of the Wars. The defeat for the Yorkists was not great in terms of lost men, but was a political disaster.

Warwick had left Henry VI under the guard of Lord Bonville and Sir Thomas Kyrell. The Lancastrian officers immediately arrested them and Henry was returned to his wife and son. Bonville and Kyrell were later executed.

With the king again in their possession and the Yorkist army scattered, the way to London lay open to the Lancastrians. It was time for the Yorkists to regroup.