Mr Henry Dennis Witt was born at Cross House, Southampton, Hampshire, England on 14 December. 1874 and was baptised on 10 January the following year.

He was the son of George Witt (b. 1845), labourer and master bricklayer, and Ellen Jane Sillence (b. 1849), natives of Southampton who had married on 15 September 1867.

He had five known siblings: Alfred William George (1868-1944), William Henry (b. 1870), John Alexander (1872-1950), Ellen "Nelly" Mary Elizabeth (1876-1929, later Mrs James Albert White) and Daisy Gertrude Martha (1882-1953, later Mrs William Robert Adams).

Harry, as he was better known, and his family appear on the 1881 census as residents of 22 Chantry Road, Southampton. By the time of the 1891 census the family are scattered around different addresses, suggesting a split in the family: his father and brother are at 15 Anglesey Terrace, his sister Nelly is working as a servant at 3 Latimer Street and Harry and his mother are residing at 27 Coleman Street and he is described as a rivet boy.

By the time of the 1901 census his mother was co-habiting with another man, dock labourer Charles Hallett (b. 1862) at 21 Coleman Street; also living there was her daughter Daisy. There is no record of Ellen Witt ever marrying Hallett and it is probable that the arrangement was common-law; when she died on 31 January 1911 she was listed under her married name of Witt. Harry's father died on 6 October 1902. 

When Witt went to sea is not clear but he would be absent from the 1901 census. He was not originally signed on for Titanic's maiden voyage but he, together with other stokers Geer, Kinsella, Hosgood, Lloyd, Brown and Black, was taken on at the last moment as a substitute. He gave his local address as 28 Lower College Street, Southampton (the home address of his sister Nelly) and his previous ship as the Oceanic and as a fireman he could expect monthly wages of £6. Also serving aboard as a stoker was his young cousin James Norris, the son of his maternal aunt Kate Norris, née Sillence.

Harry Witt, who was unmarried, died in the sinking and his body, if recovered was never identified. He is remembered with a plaque on a grave at The Old Cemetery, The Common, Southampton. The grave number is C175, 076.

His last known surviving sibling was his youngest sister Daisy who died in Southampton on 27 March 1953. The husband of his sister Nelly, James Albert White (1875-1928), later survived the sinking of the Britannic in 1916.