Knox was educated at Bedford Modern School.
He commanded the 1st/7th battalion of the Royal Warwickshire Regiment from 1915 until his death in 1918 on the Italian Front during the Battle of Asiago (1918). The family were prominent in civil and railway engineering and had become affluent through their majority shareholding in the Haunchwood Brick and Tile Company. James was the first of nine sons who all fought in the First World War.
He worked as an engineer at Bristol Docks and was commissioned in 1899 in the Nuneaton Volunteer Company of the 2nd Volunteer Battalion, the Royal Warwickshire Regiment which in 1908 became the 7th battalion of the Royal Warwickshire Regiment.
The territorial battalion formed part of the 143rd brigade part of 48th (South Midland) Division. Knox commanded the battalion from 1915 on the Western Front, notably at the Battle of the Somme and the 3rd Battle of Ypres.
Lieutenant-Colonel (A/Lieutenant-Colonel) James Meldrum Knox, Doctorate.S.O., R. War.
Regiment Foreign conspicuous gallantry and devotion to duty in command of his battalion. He kept touch with the situation till ordered by the division to counter-attack when the enemy had broken through.
Thanks to his splendid handling of his battalion, this counter-attack was decisive, the enemy were at once held up, and after heavy fighting were driven back with severe losses, several hundred prisoners being captured and the front line restored. He was also mentioned in despatches on five occasions.
In November 1917, the Brigade was transferred to the Italian campaign and saw action at the Montello Front and on the Asiago Plateau.
James Meldrum Knox was killed on 23 September 1918. A private in the battalion recorded the news: "September 23rd - Early this morning we received the very bad news that Lieutenant-Colonel Knox, the commanding officer of the battalion had been killed by a shell in his dug-out at headquarters on the San Sisto Road.
He had commanded the battalion since 1915 and was a very decent man and respected by everyone.
He was not a parade soldier and did not care for drill and show, but was always at hand in the line, knowing no fear but never sending anyone where he wouldn"t go himself. He is buried at the Granezza British Cemetery near Vicenza, and there is a memorial to him there.
After his death, Knox"s parents commissioned his portrait by the Birmingham artist Edward Samuel Harper. The painting hangs in the Nuneaton Museum and Art Gallery.