Beckwith-Smith was born on 11 July 1890 at 24 Walton Street, Chelsea to stockbroker Beckwith Smith and Georgina Butler Moore. His education took in Warren Hill School at Eastbourne, Eton and Christ Church, Oxford. In 1910 he was commissioned into the Coldstream Guards. He served with the Guards throughout the First World War, eventually becoming a staff officer in the Guards Division. On 4 October 1914, whilst 1st Guards' Brigade was holding trenches opposite the German line at the River Aisne, Beckwith-Smith was ordered by Brigadier General Charles FitzClarence to carry out a nighttime raid against a German position known as 'Fish Hook Trench'. This was the first British trench raid of the First World War. Beckwith-Smith was still just a lieutenant at the time and the raid was considered to be a striking success. On the front of the 1/Coldstream, just east of the Troyon factory road, the Germans had run out a sap, and it was decided to fill it in. At 8 P.M. a platoon of the battalion, led by Beckwith-Smith, crossing the hundred yards of No Man's Land, rushed the trench with the bayonet. The award of the DSO was reported in the Edinburgh Gazette on 13 November 1914, Now a Captain, Beckwith-Smith was awarded the French Croix de Guerre in 1917. In the same year Captain Beckwith-Smith was awarded the Military Cross.
Between the wars
After the war Beckwith-Smith commanded the University Training Corp at Oxford University. While commanding the Officer Training Corp the university conferred an honorary MA on him. The Times recorded his appointment as 'Officer Commanding the Welsh Guards Regiment and Regimental District' from 1 October 1934. In his capacity as Lieutenant-Colonel commanding the Welsh Guards he participated in the Royal Procession at the 1936 Trooping the Colour and again the following year. He spent 14 months serving in India in command of the Lahore Brigade.
In early 1942, after many weeks at sea, Beckwith-Smith's division was landed at Singapore. Japanese forces invaded Singapore Island on 8 February. Because of the defensive strategy implemented by the Allied commander, Lieutenant General Arthur Percival, most of the British 18th Division saw little or no action. Percival surrendered all British and Commonwealth troops at Singapore on 15 February, including Beckwith-Smith and his division. He was reported just prior to capture as being 'quite undisturbed by the calamity, continuing his duties even when the roof of his headquarters was burning over his head. Prior to his being sent to Formosa in August 1942, Beckwith-Smith sent a message to his men: On 11 November 1942 Merton Beckwith-Smith died at Karenko Camp of diphtheria as a prisoner of war. A report in The Times reported that the official Japanese news agency said Colonel Robert Hoffman of the US Army was with him, along with other British generals, when he died. In 1946 the Imperial War Graves Commission exhumed all the Taiwan prisoner of war remains and reburied them in the Sai Wan War Cemetery in Hong Kong. Many years later his grave was identified by Jack Edwards on the request of Diana, Princess of Wales.
Personal life
Beckwith-Smith married Honor Dorothy Leigh on 14 March 1918 at St. George’s Church, Hanover Square in London. He lived at The Manor House, Stratton Audley and Aberarder, Inverness. He had four children: Peter, Rosemary, Sarah and John. His grandchildren include the British racehorse trainer Nicky Henderson, and Anne Beckwith-Smith, Princess Diana's Lady-in-Waiting.