Belmore became Governor and Commander-in-Chief of New South Wales on 8 January 1868 at a time when the position was not yet just a figurehead for the colonial government and he was still an imperial officer responsible to the British government.
On 12 March 1868 he was attending a picnic with the visiting Prince Alfred at the Sydney beachside suburb of Clontarf when Henry James O'Farrell shot Alfred in the back and claimed to have intended to shoot Belmore as well.
Although Belmore did not see the incident, he arranged for Alfred's transfer to hospital for treatment and passed on to the colonial government the Prince's request for clemency for O'Farrell, which was ignored.
He worked effectively to calm the sectarian passions unleashed by the incident.
Belmore succeeded in having the Audit Act 1870 passed, which established the principle that government expenditure had to be authorised by appropriation through both houses of parliament, which had not been the practice until that time.
He found the Sydney summers oppressive and therefore rented Throsby Park, near Moss Vale, as his country house.
He resigned to protect his wife's health and to resume his parliamentary career, and left Sydney on 21 February 1872.