He was also a senior official within the administration of the newly-established colony of New Zealand, following the proclamation of sovereignty by William Hobson (on behalf of the British Crown) and the signing of the Treaty of Waitangi in 1840.

[3] Coates practiced law in Jamaica[4] and worked within the government of the British West Indies[5] before leaving to settle in New Zealand.

[10][11][12] Also arriving from England via Sydney on the Chelydra that day was Sarah Anne Bendall (1819–1892[13]) who subsequently became Mrs Coates in the second recorded wedding in Auckland.

[14] The wedding took place in the drawing room at Government House on 24 June 1841, with the bride being given away by William Hobson, the Governor of New Zealand.

[21] On 19 April 1841, in the first public land auction in what was to become Auckland City, Coates purchased two of the initial 119 sections put up for sale.

Then in the first sale of suburban and country land on 1 September 1841, he purchased a small farm (12 acres) in partnership with captain William Cornwallis Symonds.

On 16 November 1840 Lieutenant-Governor William Hobson appointed Coates as his private secretary, a role which had previously been performed by Freeman as chief clerk.

[24] On 3 May 1841 Coates relinquished his role as private secretary when Hobson (now governor, rather than lieutenant-governor, as Queen Victoria had by this time decreed New Zealand to be a separate colony from New South Wales, and had appointed Hobson as governor) appointed Coates as the first clerk of the executive[25] and legislative councils.

[34] When Robert FitzRoy took office as governor in late 1843 he appointed (with effect from 15 January 1844) Coates, together with the newly appointed Colonial Secretary, Andrew Sinclair, and Registrar of Deeds, Robert Appleyard Fitzgerald, as "Commissioners, pro tempore, to examine the public accounts of the colony".

[43] After some debate about whether it was appropriate for the House to appoint its Clerk and Sergeant-at-Arms, it was decided that the Administrator of the Government (Robert Wynyard, who was head of the Executive branch of government from January 1854 to September 1855, following the end of George Grey's first term as governor and prior to the arrival of Governor Thomas Gore Browne) should be asked to make appointments to these positions.

[64] Coates' third child Georgiana Sophia, born 1846, married Canon Charles Moseley Nelson,[65] who was the Vicar of St Paul's Church, Auckland for 38 years.

[66] The National Library of New Zealand holds a sketch by Charles Heaphy which depicts Rev Nelson proposing to Georgiana ("Sophy") at the Freemason's picnic.