William Sefton Moorhouse was baptised on 18 December 1825 at Knottingley House, Yorkshire, England, the oldest son of William Moorhouse, a magistrate, and his wife, Ann Carter. He went to sea as a youth in coal-carrying vessels owned by his father, then studied law at the Middle Temple, was called to the Bar in 1849, and practised for three years on the northern circuit. On 12 August 1851 William and two brothers, Benjamin and Thomas, sailed on the Cornwall for Canterbury, New Zealand, having taken out a Canterbury Association land order, which they sold to the Reverend Joseph Twigger just before arriving at Lyttelton on 10 December 1851. After their arrival they bought a land order from a private owner and selected 50 acres at Moa-Bone Point, Redcliffs, Christchurch.
Early in 1852 William Moorhouse went to Wellington, where he was admitted to the Bar on 26 January 1852. He and Benjamin soon after rode over part of the North Island looking at land, but returned to Lyttelton, where Benjamin later took up a sheep station. About 1853 William bought the brig Gratitude and traded to Australia both on his own account and under charter for others.
Moorhouse's involvement in Canterbury politics began with the election for the province's first superintendent, in July 1853. To oppose the candidacy of James Edward FitzGerald, spokesman for the Canterbury Association's land policy, Moorhouse nominated James Campbell, commissioner of Crown lands for the area outside the original Canterbury block, and an advocate of cheap land. Campbell, in spite of being technically disqualified from standing, topped the polls in Akaroa and Lyttelton, but FitzGerald's victory in Christchurch ensured his election. Moorhouse himself failed to win election to the provincial council in September 1853, although in 1854, against the pastoralist R. H. Rhodes, he won the Akaroa seat in the House of Representatives.
Late in 1853 Moorhouse and his brothers went to Wellington, intending to sail on the Tory for Victoria, Australia. While they waited for their ship, Jane Anne Collins, to whom Moorhouse had been unofficially engaged, arrived unexpectedly from England. The couple were married in Wellington on 15 December 1853. The Moorhouses' first home after their marriage was a tent at Yan Yean at the Victorian goldfields, where the brothers took up a contract to build a waterworks. William returned to Auckland with Jane to attend the General Assembly in 1854 but went back to Victoria, living for a time at Prahran, near Melbourne.
In March 1855 Moorhouse was elected to the Canterbury Provincial Council, remaining a member until 1857. FitzGerald did not stand for re-election as superintendent that year, and Moorhouse, with the support his lifelong friend John Ollivier, won an easy victory over FitzGerald's favoured candidate, Joseph Brittan; Moorhouse's chief support came from Lyttelton, Kaiapoi and country areas.
As superintendent, Moorhouse announced his intention to press vigorously for a railway tunnel from Christchurch through the hill to Lyttelton. FitzGerald, by now Canterbury's agent in England, opposed the plan, but Moorhouse gained the support of the council and of the Stafford government to raise a loan of up to £300,000. When the English contractor withdrew, Moorhouse obtained the consent of the council to seek both a new contractor and a public loan in Australia, and left for Melbourne in January 1861. In both these missions he was successful. Moorhouse made a triumphant return to Canterbury in April. He was met at the Heathcote ferry by a cavalcade of 100 horsemen and a band playing the popular tunes 'Oh Willie, we have missed you' and 'Hail the conquering hero comes'. He was drawn in a carriage to the Christchurch town hall where he addressed the crowd, and was able to say that the Union Bank of Australia, whose local manager had not been sympathetic to the council's needs earlier, had now relented.
FitzGerald had meanwhile returned to Canterbury, still annoyed at his defeat on the tunnel scheme, and more so at the form of its financing. He quickly secured support to begin a newspaper, the Press, committed to opposing both Moorhouse and the railway tunnel; he had little success. On 15 May 1861 the provincial council formally complimented Moorhouse on his achievement, a compliment echoed by Lord Lyttelton, the chairman of the Canterbury Association, on his visit to Christchurch in 1868.
Moorhouse seems not to have fully realised his potential after his persistence and success with the railway tunnel. He was re-elected as superintendent in August 1861, but caused difficulty for himself by his unorthodox method of obtaining the land necessary for a riverside jetty and railway station at Ferrymead. The acting treasurer, R. J. S. Harman, resigned rather than authorise the necessary payments, an event which caused the new council to hold an inquiry. Led by Moorhouse's old opponent, Joseph Brittan, they nearly carried a vote of disapproval of the actions of the superintendent, but his opponents were chiefly rural members who did not want the tunnel. On this, and on a later occasion when Moorhouse, again at no personal gain, bought from Edward Jerningham Wakefield land required for the Christchurch railway station, he displayed an indifference to accepted procedures in public politics. Moorhouse's popularity was seen in his unopposed re-election as superintendent in April 1862. At that time Henry Sewell lamented that Moorhouse had complete 'command of the Democracy'.
Unexpectedly, Moorhouse resigned his office in February 1863 because of his difficult financial circumstances; curiously, he had in December 1862 vetoed an ordinance increasing the superintendent's salary from £700 to £1,500. Even the Press was complimentary on the occasion of his retirement, commending him for his undeviating faith in Canterbury. Moorhouse re-entered the provincial council in March 1863 as member for Kaiapoi, and on 27 October in the same year joined Samuel Bealey's executive, just when there was a strong rumour that Bealey was contemplating retirement. But FitzGerald encouraged Bealey to remain, and when his executive resigned, a new capable one was found in its place. Moorhouse, in opposition, watched his opponents continue his policies, even the implementation of the great southern railway for which Moorhouse had reserved land as early as 1859. For the rest of the period of the Bealey administration, Moorhouse was no more than an active critic of the policies of his successor. On 1 December 1863, when the Ferrymead railway was opened, Moorhouse rode on the engine waving to the large crowd.
In 1865, after the discovery of gold, Moorhouse was drawn as if by a magnet into Westland politics. The construction of a costly dray road across the Southern Alps had made it possible for him to travel as the only passenger, sitting with the coach driver, on Cobb and Company's first venture over Arthur's Pass to Hokitika. He was just in time to make the required opening speech at his public nomination as the first parliamentary member for Westland. He won the subsequent poll by 40 votes. A month earlier, in February, he had won election for the seat of Mt Herbert, near Christchurch, but he opted in favour of Westland.
Well before Bealey's term as superintendent lapsed, Moorhouse indicated his intention to contest the next election. He was opposed by W. T. L. Travers and by FitzGerald's choice, J. D. Lance. Moorhouse declined to make an issue of squatters or land regulations, and was consequently supported by some pastoralists. He stood simply on his claim that he had 'first taught the public the leading idea of progress'. He won handsomely. On 13 October 1866 Moorhouse and members of the government attended the ceremonial journey over the first 13 miles of the railway south from Christchurch. The Lyttelton tunnel line was opened for passenger transport on 9 December 1867.
In the General Assembly Moorhouse was baulked in his strong attempt to obtain wider representation for Westland. Throughout 1867 he had to grapple with discontent between eastern Canterbury and the West Coast over public expenditure and the burden of public debt. This division led to the creation of Westland as a county separate from Canterbury. In the contest on the terms of separation, Moorhouse was able to amend the bill so that the division of the Canterbury provincial debt fell heavily on Westland. For this he was burned in effigy in the street at Hokitika. He continued to represent Westland in Parliament until he resigned the seat on 20 February 1868.
Moorhouse found his final superintendency difficult. He differed with the council over the powers of the superintendent, and was criticised for unauthorised expenditure. Nevertheless, his resignation on 7 April 1868 was, once again, prompted by acute financial trouble; he was probably facing bankruptcy as a consequence of costly land purchases, and certainly felt the need to repay his creditors. By 1864 he had a large overdraft with the Bank of New Zealand and his failure to redeem one of six bills of exchange provided by S. B. Stiffe led him to file for bankruptcy in 1870.
Moorhouse, against his own best judgement, stood against William Rolleston for the superintendency in April 1870, failing by 897 votes to 1,800. Clearly the much-feared democracy had changed its mind. In the campaign he said that he was not the man he had been, and possibly the diabetes which dogged his later life was already troubling him. He had an indifferent legal practice and his little farm somewhere beyond Spreydon did little but provide fresh eggs, butter and milk for his long-suffering wife. In October 1870 he obtained the position of registrar in the Crown Lands Department in Wellington, and soon after was made registrar general, charged with implementing the new system of land registration for New Zealand. Perhaps for the first time Jane Moorhouse had a steady family income. But Moorhouse gave up the position in order to contest the parliamentary seat of Egmont, vacated by William Gisborne in 1872, offering himself as an ardent supporter of Julius Vogel, whose development programme he had anticipated a decade earlier. However, he was defeated by Harry Atkinson, who had strong local support, in October 1872.
Moorhouse won the mayoralty of Wellington in 1874 but declined the honorarium of £200. He regained a seat in Parliament as the third member for Christchurch in December 1875, and after the dissolution in 1879 obtained the Ashley seat, which he held until his death in Wellington on 15 September 1881 from diabetic sepsis. He was survived by Jane Moorhouse and their five children.
Moorhouse commanded firm friendships, notably with John Ollivier, who arranged his farewell in Christchurch on 2 December 1870, when he was presented with a tankard, and Jane with a tea and coffee service. Ollivier, recalling Moorhouse's day of triumph on returning from Victoria, had inscribed on the tankard in his own hand, 'Oh, Willie, we shall miss you.' A bronze statue erected to his memory, the work of R. A. Lawson, stands in the public gardens close to the street later known as Rolleston Avenue.
His name is perpetuated in Moorhouse Avenue in Christchurch, and in the Moorhouse Range and Sefton Peak in the Southern Alps, both bestowed by Julius von Haast, whom Moorhouse brought to Canterbury as provincial geologist. In Wellington his name is perpetuated in Moorhouse and Sefton streets, Wadestown.