The volunteers of the Lothians served overseas during the period 1914-18. Many of the regiment's original complement were promoted into other units, especially in the service and technical branches of the Army as they expanded to meet the demands of the war.

This is an olive green or khaki private soldier's tunic or coat with blue collar and epaulettes and a white cord lanyard on the left shoulder. It fastens in front with five large brass buttons marked LOTHIAN AND BORDER HORSE YEOMANRY, shoulder clips L&BHORSE, and wheat sheaf insignia on the collar.

The Lothians and Border Yeomanry was designated on mobilisation as divisional cavalry for two larger Territorial Army formations during the First World War. In the conditions of the Western and Salonika Fronts, that role was limited and parts of the regiment were used in infantry and communications roles.