The 3rd Cavalry Brigade was a brigade of the British Army. The brigade served in the Napoleonic Wars, the Boer War and the First World War where it was assigned to the 2nd Cavalry Division. In 1914, at the start of the First World War, the brigade was a pre-war formation based at The Curragh in Ireland and originally consisted of three cavalry regiments, and a Royal Engineer signal troop. After the declaration of war in August 1914, the brigade was deployed to the Western Front in France, where an artillery battery joined the brigade the following September and a Machine Gun Squadron in February 1916.