Mr John Dickson Longmuir was born in Walthamstowe, London, England in mid-1892 and baptised on 13 September the following year.

He was the son of John Dickson Longmuir (1870-1909) and Florence Violet Wells (1870-1901). His father was a native of Bathgate, Lothian, Scotland and his mother was from Islington, London; they had married in Islington on August 16, 1891. Prior to their marriage his father was listed as a boarder on the 1891 census of England living at 17 Canonbury Road, Islington and was described as a bank clerk. 

Longmuir had two siblings: Percival William (b. 1894) and Gordon James (b. 1898).

John's mother passed away towards the beginning of 1901 and on the census taken that year John, his widowed father (still listed as a bank clerk and as married) and his brothers were listed at the home of his maternal grandmother Susan Wells, address 6 Vicarage Terrace. His father was remarried the following year to Emily Garner (b. 1879) in Newport Pagnell, Buckinghamshire, his new bride's birthplace, and the couple settled on the Isle of Wight and had a daughter named Hilda Constance(1) in 1907. 

Unfortunately, John's father passed away in 1909 and his stepmother and stepsister seemingly removed themselves from John and his brother's lives and returned to Buckinghamshire; the pair appear on the 1911 census living at 37 Duncombe St, Fenny Stratford, Bletchley. 

John was just seventeen by the time both his parents had passed away and he and his brother Percival went to sea around this time. Percival was shown on several voyages in 1909 through 1910 working as an able seaman aboard the Ivernia, working out of Liverpool. Neither men appear on the 1911 census and the younger brother Gordon's whereabouts at the time are uncertain. 

When he signed-on to the Titanic on 4 April 1912 Longmuir gave his address as 130 The Crescent, Eastleigh, Southampton. His previous ship had been the Oceanic and as a pantry steward he received monthly wages of £3, 15s.

John Longmuir died in the sinking and his body, if recovered, was never identified.

His brother Percival would later join the Black Watch of the Royal Highlanders. He was killed in action on 19 July 1916 and was buried in France. 

His brother Gordon also served during WWI, he with the Somerset Light Infantry. He later became a chemist and was married in 1930 and raised a family, spending much of his life in Harrow, London. He died in Hitchin, Hertfordshire on 29 March 1981.