The regiment was formed on the creation of the Territorial Force in April 1908 and placed under orders of the 1st South Western Mounted Brigade. It was headquartered at Bath with the squadrons being headquartered as follows:
- A Squadron: Bath (with drill stations at Bathampton, Farmborough, Frome, Mells and Road)
- B Squadron: Weston-super-Mare (Axbridge, Clevedon, Langford and Nailsea)
- C Squadron: Shepton Mallet (Queen Camel, Ston Easton, Wells, Wincanton and Castle Cary)
- D Squadron: Bristol (Queen Charlton, Barrow Gurnmey and Keynsham).
1/1st North Somerset Yeomanry
- August 1914 : moved with brigade to Sussex after mobilising but was then ordered independently to France, landing on 3 November.
- 13 November 1914 : came under orders of 6th Cavalry Brigade in 3rd Cavalry Division.
- 13 May 1915 : regiment suffered heavy losses in defending a German attack near Bellewaarde (Ypres)
- 10 March 1918 : left division, initially to be converted to infantry. Two days later this was changed to a plan to merge with Leicestershire Yeomanry to form a machine gun battalion. This too was altered and the regiment returned to the Cavalry Corps.
- April 1918 : regiment broken up, one squadron going to each of the regiments in 6th Cavalry Brigade (1st Dragoons, 3rd Dragoon Guards and 10th Hussars)
2/1st North Somerset Yeomanry
- Formed as a Second-Line regiment in September 1914, coming under orders of 2/1st South Western Mounted Brigade. Moved to Calne (Wiltshire) in May 1915 then to Canterbury in September 1915.
- March 1916 : moved to Colchester, brigade coming under 4th Mounted Division and being renamed 15th Mounted Brigade. Moved to Morpeth, back in Northumberland.
July 1916 : converted to a cyclist unit under orders of 6th Cyclist Brigade in 2nd Cyclist Division.
- November 1916 : moved to Ipswich area merged with 2/1st Wiltshire Yeomanry to form 10th (Wiltshire and North Somerset) Yeomanry Cyclist Regiment, under orders of 4th Cyclist Brigade.
- March 1917 : resumed original identity, still in 4th Cyclist Brigade. Moved to Wivenhoe by July 1917 and went in November to Walton-on-the-Naze.
- Early 1918 : moved to Ireland and stationed at Dublin where it then remained.
3/1st North Somerset Yeomanry
- Formed as a Third-Line training unit around May 1915.
- Summer 1916: affiliated to 11th Reserve Cavalry Regiment at Tidworth.
- February 1917: absorbed into 6th Reserve Cavalry Regiment at Tidworth.
In the 1917 renumbering of the Territorials, the North Somerset Yeomanry issued numbers from the block 165001-170000. Corps of Dragoons.