On 12 March 1868, he shot and wounded Prince Alfred, Duke of Edinburgh, the second son and fourth child of Queen Victoria.

O'Farrell had briefly been employed by his brother, a Melbourne solicitor, who had offices in Ballarat, and is therefore sometimes described as a law clerk.

[citation needed] In 1868, Prince Alfred, then 23 years old, went on a world tour, which included the first royal visit to Australia.

The assassination attempt outraged the attending crowd, and O'Farrell was severely beaten and nearly lynched by the mob before police arrested him and removed him to safety.

The Prince was hospitalised for two weeks, and cared for by six nurses trained by Florence Nightingale, who had arrived in Australia that February under Matron Lucy Osburn.

The attack caused great embarrassment in the colony, and led to a wave of anti-Catholic and anti-Irish sentiment, directed at all Irish people, including Protestant Loyalists.

In order "to raise a permanent and substantial monument in testimony of the heartfelt gratitude of the community at the recovery of HRH".

When Canadian politician and anti-Fenian D'Arcy McGee was killed by another alleged Fenian on 7 April, the excitement increased.