[20] Campbell was commissioned by Governor Thomas Gore Browne as a captain in the Auckland Battalion of the New Zealand Militia with effect from 3 December 1856.

[24][25][26] As battalion adjutant Campbell regularly issued instructions to militiamen via newspaper advertisements in the Daily Southern Cross and New Zealander.

[31][32][33] Campbell resigned from the Auckland Rifle Volunteers in late 1862[34][35] (possibly due to the birth in August 1862 of his first child, a son,[36] who did not survive) and was reappointed, with the Rank of Major, with effect from 23 June 1863.

[44] In a 1908 letter to the Manawatu Standard, Campbell wrote an account of a battle that took place near Tuakau in September 1863, while he was commander of the Auckland Rifle Volunteers.

[45] On 29 December 1851 Campbell applied for a sheep and cattle run on Crown land on the Wai-au Ua Plains in Canterbury.

[46] However it appears unlikely that Campbell actually farmed in Canterbury because on 24 June 1853 he was appointed Chief Clerk of the Office of the Auditor General in Auckland.

[48][49][50] In 1856 the Wellington Independent newspaper, in a series of articles about the General Assembly, described Campbell and his work as Clerk of the House: "The Clerk in suit of solemn black and scarlet stockings, sits immediately under the Speaker's chair, at the head of the long table which runs through the center of the House for a third of its length.

Charged with the whole of the documentary business of the House, he revels in red tape and pigeon holes, and ought to have (we have no doubt: Mr Campbell has) the organs of order and memory enormously developed.

His business in the House consists in taking accurate minutes of the proceedings, recording divisions, reading documents, etc.

This case addressed the important issue of whether the Clerk of the House was required to produce in court potentially libelous documents that had been tabled in Parliament.

With the Speaker's (Sir David Monro) concurrence, Campbell expressed the opinion that to do so without an order from the House would be likely to be a breach of Parliamentary Privilege.

"[77] Campbell's letter of resignation was read in the House by the Speaker Sir George Maurice O'Rorke, who noted that on becoming Clerk of the House Campbell had hardly any precedents to guide him, but by his "painstaking, accurate and methodical character [he] managed to bring the system of recording our proceedings and printing our statutes to very great perfection".

[87] Campbell was a keen hunter and fisherman and in April 1873, more than a decade after the introduction of red deer into New Zealand, he is reputed to have shot the first stag in the wild.

[90] Campbell died at his daughter Jessie's home (where he resided in his later years) in Awahuri at the age of 87 on 27 September 1911[91][92] and is buried at Feilding Cemetery.