Denis Lynch was born in Portsmouth, Hampshire on 29 November 1910, the son of Petty Officer Denis Lynch, RN, and Hilda Mary Lynch (née Westrup). He joined the Royal Navy as an Engine Room Artificer Apprentice on 2 August 1926. On 23 September 1941 Engine Room Artificer Second Class Denis Lynch was serving in HMS TIGRIS.

Denis Lynch was promoted to Acting Warrant Engineer on 1 October 1942 and was appointed to HMS SYRTIS on 28 December 1942 as the Engineer Officer on commissioning. SYRTIS left Lerwick on 16 March 1944 for a patrol off the Norwegian Coast and, on 20 March, was ordered to an area in the vicinity of Bödo. She conducted attacks on enemy vessels in the area on 22 March. SYRTIS was ordered to leave patrol on 28 March but failed to return to Lerwick. An air search was conducted but no sign of her was found. Mines are now known to have been laid in the area in which SYRTIS was working and it is almost certain that the submarine was lost with all hands by striking a mine off Bödo between 22 and 28 March 1944

Denis Lynch was the husband of Marion Jean Lynch. He is commemorated on the Portsmouth Naval Memorial on Panel No. 81, Column No. 1.