Mr William Thomas Carson McReynolds was born at 22 Rotterdam Street in Belfast, Ireland (modern-day Northern Ireland) on 1 September 1889. 

He was the son of Thomas McReynolds (b. 1861), a fireman, and his wife Annie Carson¹ (b. 1862) who hailed from counties Tyrone and Down respectively and who had married in St Anne's Church, Belfast on 25 February 1887.

Coming from a Presbyterian household, William had six known siblings: Margaret Jane Crozier² (b. 15 February 1888), Martha³ (b. 12 December 1890), George Frederick (b. 26 July 1893-1946), Joseph Ernest (b. 3 November 1895), Annie Mary "May" (b. 19 May 1899) and Sarah "Sadie" Wilson (b. 2 April 1903). 

William, as per the birth records of he and his siblings, spent much of his earlier childhood at 22 Rotterdam Street; he appears with his family on the 1901 census living at 7 Laganview Street, Pottinger, East Belfast, Co Down and his father was, at the time, described as a stoker in the iron works. Whilst William was still described as a schoolboy and aged 11, his 13-year-old sister Mary was already in employment as a machinist.

Following school William was apprenticed to Harland & Wolff's Engineering department. He joined the White Star Line on 25 March 1912 as a junior engineer and was also a member of the Lodge Temperance Dart Club. By the time of the 1911 census of Ireland William was described as an engineer and still unmarried and living with his parents, then at 20 Rotterdam Street, Pottinger.

He boarded Titanic in Belfast on 2 April 1912 and re-signed for the maiden voyage on 6 April in Southampton, giving his address as Lagan Villas, Belfast. The Titanic was his first ship and as Junior Sixth Engineer he received monthly wages of £8, 10s.

William McReynolds was lost in the sinking and his body, if recovered, was never identified. He is commemorated on various Memorials dedicated to Titanic's Engineers and is also listed on the Titanic Memorial located in the grounds of Belfast City Hall.

His parents remained in Belfast; his mother died on 15 October 1934, still a resident of Rotterdam Street, whilst father died 9 October 1938, then a resident of Baltic Street; they are buried in Dundonald Cemetery in east Belfast.