Sydney Carlin was born in Hull, the son of William Carlin, a drysalter. By 1901 he was a boarder at a small private school in the village of Soulby, Kirkby Stephen, Westmoreland. He enlisted with the 18th Royal Hussars in 1908, but he bought himself out and resigned in December 1909 for the sum of £18. In 1911 he was working as a farm labourer at Frodingham Grange, North Frodingham, Yorkshire.
He re-enlisted on 8 August 1915; the army refunded half (£9) of the money he had bought himself out with in 1909. Serving in Belgium with the 18th Royal Hussars he was awarded the Distinguished Conduct Medal on 5 August 1915, and was later commissioned as a second lieutenant in September 1915 and made a lieutenant in May 1916. He lost a leg serving in the Battle of Longueval/Delville Wood, on the Somme in 1916, while commanding a Royal Engineers Field Company section holding a trench against repeated German counter-attacks. For this action he was awarded the Military Cross in October.
Extraordinarily, he joined the Royal Flying Corps in 1917, following his recovery. On 12 March 1918, Carlin was seconded from the Royal Engineers to the RFC. After serving as an instructor at the Central Flying School, he was posted in May 1918 to No. 74 Squadron RFC flying S.E.5As, where he earned his nickname "Timbertoes". Carlin is recorded as an ace balloon buster, with five balloons downed; he was also an ace against aircraft, with four machines claimed destroyed, and one aircraft 'driven down out of control'. His exploits earned him the Distinguished Flying Cross.
On 9 August 1918 Lieutenant Carlin was promoted to temporary captain. In early September he was involved in a mid-air collision with his commanding officer, Major Keith Caldwell, but was relatively unscathed.
On 21 September Carlin was shot down over Hantay by Unteroffizier Siegfried Westphal of Jasta 29 and held as a prisoner of war. He was repatriated on 13 December 1918 and admitted to the RAF Central Hospital on Christmas Day 1918. Carlin relinquished his commission on "account of ill-health contracted on active service" on 7 August 1919. and retained the rank of lieutenant.
On 1 January 1924 Carlin was promoted from flight lieutenant to squadron leader. Nevertheless, in 1924, Carlin departed Britain for Mombasa aboard the SS Madura. He was listed on the passenger list as an "agriculturist". He farmed for some years in Kenya.
From 20 May 1931 to 8 August 1935 Carlin served as the Justice of the Peace for Kisumu-Londiani District, Kenya.
On re-enlistment to the RAF he was graded as a probationary pilot officer on 27 July 1940. He made pilot officer in September 1940, flying as an air gunner in Defiant aircraft with No. 264 Squadron RAF and later No. 151 Squadron RAF. He also made several unofficial trips as an air gunner with No. 311 (Czech) Squadron, flying Wellingtons.
Carlin was injured in action at RAF Wittering during an enemy bombing raid on 7/8 May 1941, and died in Peterborough on 9 May 1941. He is memorialized on the Screen Wall, Panel 1, Hull Crematorium.