William George Niccoll Searancke, later known as William Nicholas Searancke, was baptised on 11 April 1817 at St Albans Abbey, Hertfordshire, England. He was the son of Harriet Smith and her husband, Francis Searancke, a brewer. William worked for his elder brother, Samuel Stephen Searancke, county engineer of Meath, Ireland, and was then employed at a Windsor survey office.
Searancke arrived at Port Nicholson, New Zealand, on the Brougham on 9 February 1842 as a second assistant surveyor with the New Zealand Company and was sent to work in Taranaki. In November he was dismissed for incompetence and insubordination. An attempt to regain his position was unsuccessful, but he remained in Taranaki, at New Plymouth. In September 1845 Searancke and a man named Spencer had property taken in retribution by local Māori who were outraged at the behaviour of the two men towards women of Puketapu. By March 1847 Searancke had become an itinerant trader, possibly based at Ahuriri (Napier). He is said to have joined the 1849 Californian goldrush.
By about 1850 Searancke was living in the Waikato region, probably near Te Kōpua, where he was adopted by Ngāwaero hapū of Ngāti Maniapoto. He formed a liaison with a woman of Ngāwaero, but, as she was unable to bear children, she was replaced by Hāriata Rangitaupua. The four children of Hāriata and William Searancke were born between 1851 and 1857. In 1856 Searancke was again engaged in surveying, this time in the South Auckland area, and in April that year he was appointed as surveyor in the Land Purchase Department. In the course of his work he produced intelligence reports on the developing King movement.
By early 1858 Searancke had been transferred to Wellington province as district commissioner in the Land Purchase Department. He negotiated major purchases in the Wairarapa, Manawatū and Horowhenua areas and became notorious for making secret deals and breaking promises. Donald McLean, chief land purchase commissioner and native secretary, recognised the value of Searancke's contacts among Waikato and Ngāti Maniapoto at a time when Pākehā were increasingly fearful of the King movement and sent Searancke back to Waikato in early 1861 as district commissioner. He was transferred to Whāngārei in 1862, where he married Susan Jane Glynn on 4 September; they were to have four daughters.
With his Pākehā family Searancke returned to Waikato in 1865, after accepting appointment as resident magistrate responsible for the area between Ngāruawāhia and Rangiriri. He was stationed at Hamilton and Ngāruawāhia at various times. From 1867 his district covered all of Pākehā-occupied Waikato, and he took over the Raglan court circuit in 1868. Searancke travelled up to 200 miles a fortnight on horseback on his court circuit and in pursuit of information on Māori activities.
Searancke played a key role in reassuring the military settlers who occupied Waikato. He investigated the frequent rumours of intended attacks on them, using his network of paid informants. In early December 1868 he heard of a plan to attack the military settlers in northern Taranaki. Although he passed the information on to Robert Parris, resident magistrate at New Plymouth, protective measures were inadequate and a number of Pākehā were killed when some Ngāti Maniapoto attacked Pukearuhe redoubt two months later.
Searancke had frequent contact with the Māori community, but he appears to have had little to do with his own Māori children. His grand-daughter, Te Puea Hērangi, later a King movement leader, saw her Pākehā grandfather only once; he was pointed out to her at a hui when she was a child.
In 1870 Searancke was relieved of his Raglan duties, and in 1871 William Mair took over his responsibilities for Māori liaison, but he continued his work as resident magistrate. In mid 1878 his status among Māori was seriously undermined when he became the victim of a practical joke. He had marked the grave of his favourite dog with a wooden memorial. This was removed and placed against the earthwork of Pōtatau Te Wherowhero's Ngāruawāhia tomb. A letter, reporting that Searancke had buried his dog in the vacant tomb, was soon circulated among Māori of Waikato, who took great offence.
Shortly afterwards Searancke was dismissed from his post as resident magistrate when John Sheehan, minister of justice and native minister, decided to purge his departments of the favourites of his old enemy, Donald McLean. Over 130 Hamiltonians signed a petition and 17 justices of the peace a memorial asking for his retention, to no avail.
Searancke next took up work as a general land agent and licensed interpreter. By January 1880 he was working for the Auckland syndicate who were attempting to buy the Pātetere block. He collected the signatures of those who were awarded a share of the block at the May 1880 sitting of the Native Land Court in Cambridge. Later he was sent to Wellington and Manawatū to gain the signatures of absentee owners.
During the 1880s and 1890s Searancke was prominent in community affairs in Hamilton. He was a Freemason, a member (and for a time chairman) of the Hamilton East School Committee, presided as a judge at several race meetings, and continued to serve as the district's coroner. He died from heart failure at Hamilton on 29 April 1904; his wife had predeceased him in 1901. At his best astute and personable, at his worst devious and unfeeling, Searancke exploited every opportunity to further his career in the administration of land and justice.