Following the breakout from Normandy, Major Cavendish's unit, the 3rd Company of the 5th Battalion of the Coldstream Guards, advanced steadily through northern France, despite fierce German opposition. When the first British Guards units liberated Brussels on 3 September, Cavendish wrote to his wife Kathleen that the scenes of joy gave him a lump in his throat. However, he could not enjoy the bustling capital for long, as the front line lay open between Antwerp and Liège. Montgomery therefore ordered the Guards armoured units to advance towards the Dutch border on 6 September. During this advance, the British units had to cross the Albert Canal, where the Germans had meanwhile blown up the bridges. That same day, the Welsh Guards managed to cross the canal via the remains of the stone bridge at Beringen.

Although the situation still looked good for the Guards, everything threatened to change quickly. On the morning of 7 September, German General Field Marshal Wilhelm Keitel had ordered a halt to the entire withdrawal of German troops on the Western Front. This required the German army to reverse the situation at Beringen as quickly as possible and push the British back across the canal.

However, German attacks on the bridgehead at Beringen failed, resulting in the town becoming a springboard towards Leopoldsburg. The intention was that the British would then reach the Dutch border via Hechtel. To that end, the Coldstream Guards were ordered to take the village of Heppen on 9 September. Under heavy artillery fire, Major Cavendish advanced towards the village at 08:45 hours. His attack took place near some farms where the Germans had dug in. At this point, Cavendish took an alternative route, but even there he came under heavy fire from the farms. Cavendish was fatally hit by a shot to the chest after storming the Mangelschots family farmhouse. Second in command, Sergeant Major Cowley, took command and captured the farmhouses an hour after the attack had started. Cowley was awarded a Distinguished Conduct Medal for this. The body of his superior, Major Cavendish, was later buried at Leopoldsburg British Military Cemetery. William Cavendish, the Marquis of Hartington, died 4 months and 3 days after his marriage.