Stephen Weart Blackwell was born in Trenton, Mercer, New Jersey on 6 September 1866 and was named after his paternal grandfather, Captain Stephen Blackwell (1808-1883).

He was the son Jonathan Hunt Blackwell (1841-1919) and Susan Weart (1841-1916), both natives of Hopewell, Mercer, New Jersey who had married there on 5 October 1865, after which they settled in Trenton.

His father, of old English ancestry, was an experienced wholesale grocer, initially working for one William Dolton before moving to New York, soon returning to Trenton and forming a partnership with his former employer. Following his partner's death he reorganised the firm as J. Blackwell & Sons. Active in local state affairs and a Democrat in his politics, he was elected in 1873 as a member of the Trenton Common Council; the following year he was successfully elected as State Senator, despite his young age, and served on various committees, including education and banks. He was also president of diverse organisations: Interstate Fair Association, Trenton Transportation Company, The Lotus Club of Trenton, Spring Lake Golf and Country Club; and was on the board of directors of numerous other bodies, including the First National Bank.

Stephen had three siblings ¹: Clara May (1867-1935), William Jewell (1869-1930) and Henry Clayton (1874-1945).

The 1870 and 1880 census records show Stephen living with his family in Trenton, the latter record showing them as residents of 227 Academy Street.

A graduate of Princeton in 1888, Stephen later worked in connection with his father's wholesale grocery business. He was married around 1901 to Emily Thomas Lake (b. 18 March 1882 ²), also of New Jersey and daughter of John Ross Lake and Martha Thomas. The couple resided in New York and would remain childless. He became a widow, however, when his wife died on 13 December 1906 as a result of typhoid.

Stephen later moved back with his parents and was shown on the 1910 census with them at 167 West State Street, Trenton and he was described as manager of the American Snuff Company. A contemporary news report (Newark Evening News, 16 April 1912) suggests that Mr Blackwell had been in ill-health for some years and that an extended trip abroad was devised to better his health.

Blackwell travelled with fellow Trentonian Washington Augustus Roebling II and the latter's chauffeur Frank Stanley on a tour of Europe in the early months of 1912. When sailing to Europe the two men became acquainted with Caroline Bonnell. They met up with Miss Bonnell and the family of George Dennick Wick while touring France and they boarded the Titanic together in Southampton. Blackwell occupied cabin "T" on the Boat Deck (ticket number 113784 which cost £35, 10s).

Miss Bonnell said she last saw Mr Blackwell in the smoking room talking with Captain Smith just shortly before the evacuation began. He was lost in the sinking.

His brothers, William and Henry went to New York with two cousins of Roebling upon receiving word of the sinking. After meeting with Miss Bonnell, the men returned to Trenton, convinced that their relatives had not survived. His sister Clara had been in Washington attending a meeting of the Daughters of the American Revolution Congress when notified of the sinking. The Trenton Evening Times also reported that Blackwell's mother had been in ill health for some time and there was concern about how she would take the news of her son, though she seemed to be holding up well once told.

Although a body, initially identified as Blackwell, was recovered (#241) it appears that his body was never found. The stone in the Blackwell family grave in Hopewell churchyard, Trenton reads simply:

"LOST AT SEA ON THE STEAMER TITANIC".

Blackwell's memorial service was scheduled for 27 April  1912, 3:00 pm at St. Michael's Episcopal Church, with the Reverend William Best Eddy presiding.

Blackwell left his estate, estimated at between $110,000 and $200,000 to his father and brothers. According to Insurance Press, his accident insurance policy paid $33,000, among the highest amounts carried by Titanic victims. Only Charles Hays at $80,000 and Frank Warren $56,000 were reported to have larger policies.

His parents remained living at 167 West Gate Street; his mother died in 1916 and his father in 1919. They are both buried, along with their children, in Hopewell Cemetery in Mercer, New Jersey.

His sister Clara never married and died in Hopewell, New Jersey on 25 April 1935. His brother William never married and died on 10 August 1930. His brother Henry was married and raised a family. He died in 1945.