John was a civil engineer in Wellington, said to be responsible for the construction of the Ngauranga Gorge and the Rimutaka Hill Road, among other key local roads.
He was in Wellington at least between 1848 and 1858, where he was involved with Ngauranga Gorge, the Akatarawa link to Waikanae and Lampton Quay, among others
Around 1848 he was appointed as a surveyor to the General Government's survey staff in Wellington, responsible (with at least one other surveyor, T. D. McManaway) for the surveying of Crown Land, at the time of some of the post-Treaty purchases of Maori land by the then General Government. In 1853 he was appointed first engineer to the Wellington Provincial Government.

In 1853 he married Mary Barton and had 3 children:
1854 - John Richard Barton
1856 - 1862 Margaret Eliza Roy
1859 - Richard Barton Roy

In 1856, he travelled to Hawkes Bay as part of his Wellington Provincial work.
In 1859 he travelled (surveyed?) through Lindis Pass and owned land on the west of Lake Wanaka (towards the Matatapu and Matukituki Rivers) for a short period. He has a number of landmarks around Wanaka named after him: Roys Peak or Mt Roy, Roys Bay, on which Wanaka is settled and Roys Peninsula, opposite the township.
On 1 May 1860 he was appointed Provincial Engineer for Otago. In July 1861 he resigned and took up land on the Ruataniwha Plains in Hawkes Bay.
* In 1862 his daughter Margaret died in Kaikorai, Dunedin
* John died on 21 Feb at Half Way Bush, Otago

Herald, 5 March 1864
We record the death of Mr john Roy, for many years Road Engineer to the Wellington Government, in which capacity and as a settler, he was associated with this province at an early date. He was much respected by a large circle of friends

Wellington Independent, 10 March 1864
ROY - On the 21st February, at his residence, Hawthornden, Half-way Bush, Otago, John Roy, Esq., late of Wellington, in the 41st year of his age
* He is buried with his daughter Margaret
* Son Richard Barton Roy is buried at Christ Church taita
* Son John Barton Roy was the 6th Mayor of New Plymouth

NZ Spectator, 17 Aug 1864
LAND SALE - On Monday last Mr J. H. Wallace sold at his Auction mart the following country properties, belonging to the estate of the late John Roy, Esq. A capital luncheon was provided, a good number of buyers were present, the bidding was spirited and though the prices obtained in some instances were low, yet on the whole they were considered to be very satisfactory, the total amount realised being upwards of £1000 (2018 equivalent of $110,318)
LOTS:
1 - Thirty-one acres, being part of Section No 25, Upper Hutt, fetched £3 10s per acre. Mr R. Gange being the purchaser
2 - Fifty acres, Western Hutt District, Lower Hutt, being section No 308 was sold for £1 5s per acre, Mr Collier being the purchaser
3 - Forty acres, section No 6, agricultural reserve, Pauhautanui, fetch £2 15s per acre, Mr Abbott being the purchaser
4 - 99 acres, part of seciton No 181, Upper Hutt, was sold for 12s 6d per acre, Mr John Martin being the purchaser
5 and 6 - 269 acres, section No 114 and 112 Upper Hutt, realised 19s per acre, Captain Stafford being the purchaser
7 - 153 acres, part of section No 2 Pakuratahi, was knocked down to Mr J. B. Wallace at 15s per acre
8 - Fifty acres, Wairarapa, Three Mile Bush Road, part of section no 134, fetched £1 7s per acre, Mr N. Levin being the purchaser
9 - Town acre, No 316, Featherston, was sold to Mr J. G. Cox for £15 10s
10 - Fifty acres, Taratahi Plain, Wairarapa, section no 198, fetched £1 1s per acre, Mr N. Levin being the purchaser
11 - Part of section No 14, Ohariu, Rawsonville, fetched £5 per acre, Mr James Sherman being the purchaser
16 - One hundred acres, section No 30, Horokiwi Valley, sold at 14s per acre
17 - One hundred acres, section No 32, Horokiwi Valley, fetched 13s per acre

His wife Mary remarried on 8 8 Sep 1866 to William Strachan Esq., M.P.C., of Tuamarina, Marlborough