Promoted major, in 1813 he commanded a corps of 400 grenadiers at the battle of Vitoria, then led a forlorn hope in the Siege of San Sebastian.

[2] He served as acting Lieutenant-Governor of Van Diemen's Land (now Tasmania) from October 1836 to January 1837, between the terms of George Arthur and Sir John Franklin.

While in this role Snodgrass despatched a Sydney mounted police detachment to pursue the Namoi, Weraerai and Kamilaroi people who had killed five stockmen in separate incidents on recently established pastoral runs in the upper Gwydir River area of New South Wales.

On 26 January 1838, a New South Wales Mounted Police detachment led by Major James Nunn murdered perhaps 40 to 50 men, women and children.

[5] The group attacked an encampment of Kamilaroi people at a place that came to be called Waterloo Creek, in remote north west New South Wales.