Joseph O'Sullivan (25 January 1897 – 10 August 1922), along with fellow Irish Republican Army (IRA) (London Battalion) volunteer Reginald Dunne, shot dead Field Marshal Sir Henry Wilson outside Wilson's home at 36 Eaton Place, Belgravia, London on 22 June 1922.

Despite a petition of 45,000 signatures, and a plea for clemency from many prominent figures at the time, including playwright George Bernard Shaw, O'Sullivan and Dunne were hanged for the murder on 10 August 1922 at Wandsworth Prison.

O'Sullivan's father, John, was originally from Bantry, County Cork, and had moved to London as a young man where he eventually became a successful tailor.

On 25 January 1915 (his eighteenth birthday) O'Sullivan enlisted into the Royal Munster Fusiliers, and later transferred to the London Regiment and served with the rank of lance corporal during the First World War and lost a leg at Ypres in 1917.

[citation needed] He became a member of the IRA detachment in London, and was named by Rex Taylor as being responsible for the execution of Vincent Fovargue as a British spy at the Ashford Golf Links, Middlesex, on 2 April 1921 with a label pinned to his body stating "Let spies and traitors beware, IRA".

Patrick O'Sullivan had also served in the London Regiment during the First World War, along with another brother, Aloysius, who was discharged from the army in 1916 suffering from shell shock.