Source: Michael Doyle Their Name Liveth For Evermore: The Great War Roll of Honour for Leicestershire and Rutland.
He was the son of Frederick Darby, a railway porter, born 1863 in Towcester, Northamptonshire and his wife Mary Elizabeth Darby (nee Bruce, married in the 3rd quarter of 1887 in the Towcester, Northamptonshire district), born 1860 in Hulcote, Northamptonshire. William Bruce was born in the 2nd quarter of 1890 in Loughborough, Leicestershire, he had one sibling, Richard Frederick J., born 1889 in Loughborough, in April 1891 the family home was at 12, Paget Street, Loughborough. In March 1901 William was residing in the family home at Sileby Lane, Mountsorrel, Leicestershire together with his father, a stone quarry labourer, his mother and siblings, Richard, Elsie, born 1891 and Agnes Dove, born 1893, the latter two siblings were both born in Mountsorrel. In the 1st quarter of 1902 in the Barrow upon Soar, Leicestershire district, William’s father died aged 38. In April 1911 William was employed as a quarry works driller, and was residing in the family home at Roecliffe Cottages, Mountsorrel, together with his widowed mother and siblings Elsie, a hosiery trade yarn winder and Agnes, a hosiery trade linker. Wiliam married Martha Agnes Kettle in the 4th quarter of 1915 in the Barrow upon Soar, Leicestershire district.
William attested into the Territorial Force to serve 4 years Service in the United Kingdom on the 31st August 1914 in Mountsorrel. He gave his place of birth as Loughborough, Leicestershire, his age as 24 years and 5 months and his trade or calling as steam driller, his present employer being the Mountsorrel Granite Company. He gave his home address as 168, Main Street, Mountsorrel. He confirmed that he was unmarried. He stated that he had served 4 years with the 5th Battalion Leicestershire Regiment, Territorial Force and was now time expired. He gave his next of kin as his mother Elizabeth Darby, his bother Frederick and sister Elsie, all of 168, Main Street, Mountsorrel, this was later changed to his wife Mrs. Darby, c/o Mrs. Kettle, New Street, Barrow upon Soar. His medical examination recorded that he was 5 foot 8 inches in height and he had a chest measurement of between 34 and 35½ inches. His vision was recorded as normal and his physical development as good. He was pronounced fit for the Territorial Force on the 31st August 1914 in Mountsorrel. His record of service began when he joined the Depot of the Leicestershire Regiment as a Private, service number 2300 on the 31/8/14. Posted to the 5th Battalion Leicestershire Regiment on the 31/8/14. Embarked to join the British Expeditionary Force in France on the 26/2/15. Landed at Le Havre on the 27/2/15. Admitted to hospital, in the field on the 13/3/15. Returned to duty with unit, in the field on the 16/3/15. Admitted to hospital, in the field suffering from a gunshot wound to the head on the 25/9/15. Admitted to the 23rd General Hospital at Etaples on the 28/9/15. Transferred to England on the 28/9/15. Embarked to join the British Expeditionary Force in France on the 10/12/15. Disembarked on the 11/12/15. Joined unit, in the field on the 22/12/15. Wounded in the field on the 16/4/16. Admitted to the 30th Casualty Clearing Station suffering from a gunshot wound IX (CU) TIC (1) on the 16/4/16. Admitted to the 5th General Hospital at Rouen, suffering from a gunshot wound XI Knee. Alluse R & Tarsus L. amptd. on the 19/4/16. Died of wounds in the 5th General Hospital, Rouen on the 20/4/16. A summary of his service records: Home Service, 31/8/14 – 27/2/15, 181 days. British Expeditionary Force, France, 28/2/15 – 27/9/15, 212 days. Home Service, 28/9/15 – 10/12/15, 74 days. British Expeditionary Force, France, 11/12/15 – 20/4/16, 131 days. Total service, 1 year 235 days. William was awarded the 1914-15 Star, British War and Victory medals. His widow was awarded a weekly pension of ten shillings to commence on the 30th October 1916.
The War Diary records: 16 Apr-16 - TRENCHES. At 11.00am officers from 25th Division came to look over trenches previous to taking over line. At 11.30am Corps Commander visited front line and supports. At 4.45pm enemy shelled front line trenches with shrapnel and high explosive, also trench mortars and bombs and rifle grenades. One of the latter unfortunately dropping in centre of trench, wounding eight men including the Battery Observation Officer who was very seriously injured. “D” and “C” Companies fatigues as before. Night quiet. Casualties 2 killed, 6 wounded.
On Friday May 5th 1916 The Melton Mowbray Times & Vale of Belvoir Gazette published the following article under the heading. “LOCAL AND DISTRICT NEWS.” – MOUNTSORREL SOLDIER KILLED. Information has been received by Mrs. William Darby, of Mountsorrel, that her husband, Private William Darby, of the Leicestershire Regiment, has succumbed to wounds received in action. Deceased was one of 130 who joined the Colours from the Mountsorrel Granite Company at the outbreak of the war, and had previously been a member of the Soar Valley Company of Territorials. The Granite Company showed their sympathy by flying flags half-mast at their works on receipt of the sad news. Private Darby had only been married five months, and was 26 years of age. His brother Fred who was reported seriously ill, is now in hospital, and on the way to recovery.

Source: Leicestershire War Memorials Project.
The following biographical information was provided by E. Freer, family member, in July 2016:

'Frederick Derby, brother of William, enlisted in the Royal Army Medical Corps on 21/04/1914 and initially served as a medical orderly in Leicester before being sent to France to join the Worcester Regiment, then the Seaforth Higlanders where he was wounded and lost his right arm. He was awarded the Military Medal and was mentioned in the London Gazette of 12 March 1918. After the war he was the village Lamp Lighter and “Knocker-up”; my mother used to accompany him and when he had a problem lighting a lamp she was pushed up the lamp post to light it! '