He was a notable campaigner for New Zealand self-government, and is generally regarded as having been the country's first premier (a post that would later be officially titled "Prime Minister"), having led the Sewell Ministry in 1856.

[2] In 1840, however, Sewell's father lost a staggering sum of money when a bank failed, and died shortly afterwards, leaving the family with a great deal of debt.

[3] Sewell remarried, probably on 23 January 1850, and made plans to emigrate with his new wife Elizabeth Kittoe to New Zealand, hoping for improved financial prospects in the colony.

Sewell personally arrived in Lyttelton, the port of Christchurch (the principal settlement in Canterbury) on 2 February 1853, hoping to sort out what remained of the colony's problems.

[3] Charles Simeon and family lived in Canterbury from October 1851 to December 1855, and they were the only people who Sewell and his wife socialised with.

The journal's editor, historian W. David McIntyre, calls it "the most absorbing and undoubtedly the fullest private manuscript relating to New Zealand in the 1850s".

[8] Sewell sought counsel from some friends, who recommended for him to stand in the rural electorate, but he did not want to oppose Guise Brittan, who had already declared his candidacy.

The complication with the town electorate was that John Watts-Russell had already received a pledge from the majority of that constituency, but there were rumours that he would not stand, and it was known that he was just about to go travelling during the time of the election campaign.

[10] In the same edition of the newspaper, James Stuart-Wortley[10] and Guise Brittan[11] advertised their candidacy for the Christchurch Country electorate.

[13] On 4 August,[14] he held a meeting at the Golden Fleece, a hotel on the corner of Colombo and Armagh Streets,[15] and addressed between 30 and 40 electors.

Here was a Gentleman who told [us] all sorts of things which a Representative ought to attend to and then declined standing himself, because of another Candidate whose intentions no one knew anything about—and who was just on the point of starting for an excursion without giving any one an opportunity of learning his sentiments about anything.The meeting expressed dissatisfaction with Watts-Russell and that they would not hold themselves bound to support him.

[23] The three candidates for the Christchurch Country electorate spoke first, with Stuart-Wortley and Wakefield winning the show of hand, and Brittan visibly offended, but demanding a poll.

Fooks was proposed by Joshua Charles Porter (a lawyer; later Mayor of Kaiapoi), and seconded by the publican Michael Hart.

When it became apparent that Wynyard regarded the appointments as temporary, and that he did not believe Parliament could assume responsibility for governance without royal assent, Sewell and his colleagues resigned.

In late 1856, Sewell stepped down as Treasurer and resigned his seat, but remained an unofficial member of the Executive Council, to return to England.

Sewell, who was a mild pacifist, believed that conflict with Māori could only properly be resolved by introducing a fair method of land purchase, one which did not involve coercion.

To this end, he twice proposed a Native Council Bill, which would have created Māori-run institutions with the authority to supervise all Māori land deals.

Later in his political career, Sewell briefly held positions as Attorney-General, Minister of Justice, and Colonial Secretary (the latter being distinct from the Premiership by this time).