Lamb met his future wife Nina Forrest in 1905 during the final term of his medical studies in Manchester and they ran away to London together that summer.

In February 1918, before he was demobilised, Lamb was approached by British War Memorials Committee of the Ministry of Information to produce a large painting for a proposed national Hall of Remembrance.

After he was demobilised in March 1919, Lamb began work on the painting, Irish Troops in the Judaean Hills Surprised by a Turkish Bombardment, which is now in the Imperial War Museum.

As well as portraits of high-ranking commanders, Lamb painted servicemen and women, operations at Old Sarum aerodrome and tank training exercises.

Throughout the winter of 1941, he was attached to the 12th Canadian Army Tank Battalion, then training in southern England, before doing a series of Auxiliary Territorial Service and Anti-Aircraft Command personnel portraits.

[1][12] The character and appearance of the composer Lewis Dodd in Margaret Kennedy's The Constant Nymph was based on Lamb, who was a gifted pianist.