Austrian commander Karl Mack had gathered the greater part of the Austrian army at the fortress of Ulm in Swabia. Napoleon swung his forces to the southeast and the Grande Armée performed an elaborate wheeling movement that outflanked the Austrian positions. The Ulm Maneuver completely surprised General Mack, who belatedly understood that his army had been cut off. After some minor engagements that culminated in the Battle of Ulm, Mack finally surrendered after realizing that there was no way to break out of the French encirclement. For just 2,000 French casualties, Napoleon had managed to capture a total of 60,000 Austrian soldiers through his army's rapid marching.

On 16 October 1834, a fire broke out in the Palace after an overheated stove used to destroy the Exchequer's stockpile of tally sticks set fire to the House of Lords Chamber. In the resulting conflagration both Houses of Parliament were destroyed, along with most of the other buildings in the palace complex. Westminster Hall was saved thanks to fire-fighting efforts and a change in the direction of the wind. The Jewel Tower, the Undercroft Chapel and the Cloisters and Chapter House of St Stephen's were the only other parts of the Palace to survive.

The largest and tallest tower is 98.5-metre (323 ft) Victoria Tower, which occupies the south-western corner of the Palace. Originally named "The King's Tower" because the fire of 1834 which destroyed the old Palace of Westminster occurred during the reign of King William IV, the tower was an integral part of Barry's original design, of which he intended it to be the most memorable element. The architect conceived the great square tower as the keep of a legislative "castle" (echoing his selection of the portcullis as his identifying mark in the planning competition), and used it as the royal entrance to the Palace and as a fireproof repository for the archives of Parliament. Victoria Tower was re-designed several times, and its height increased progressively; upon its completion in 1858, it was the tallest secular building in the world.

After the destruction of the Palace of Westminster by fire in 1834, William considered converting the palace into the new Houses of Parliament.

The Crimean War was a military conflict fought from October 1853 to February 1856 in which Russia lost to an alliance of France, the Ottoman Empire, the United Kingdom and Piedmont-Sardinia.