Nathaniel William Harrison was born at the cottage at Holywell Mill, Oxford on 5 May 1865 and baptised at St Cross Church, Holywell, Oxford on 24 June. He was the son of Nathaniel Harrison junior and Maria Frances Baxter of London, who were married at St Cross Church on 31 March 1864.

At the time of his birth Nathaniel's father was working as a coal merchant at the North-Western Wharf in Oxford together with Nathaniel's grandfather Nathaniel Harrison senior (the former miller at Holywell Mill). Nathaniel's younger sisters were also born at Holywell: Maria Frances Harrison in 1867 and Fanny Louisa Harrison in 1870.

In 1870/1 the family moved to 48 Rectory Road (then named Pembroke Street) in St Clement's, Oxford, and they can be seen living there with their 12-year-old servant girl at the time of the 1871 census when Nathaniel was aged five. His father was still working as a coal merchant.

By 1873 their address was given as 57 Rectory Road, and Nathaniel's two younger brothers were born there: Hude Henry Harrison in 1873 and Gilbert Andrew Harrison in 1876.

At the time of the 1881 census Nathaniel (15) was still at school. The family then seems to have gone down in the world: his father was now a traveller for a colliery; a college laundress Mary Belcher lived in one part of their house; and they no longer had a servant, None the less later that year Nathaniel was articled to Messrs Wilkinson & Moore and his career as an architect began. He studied at the Ruskin School of Art, and travelled in France, Belgium, and Germany.

In the 1891 census when he was aged 25 Nathaniel was described as an Architect's Managing Assistant and was still living with his parents at 51 Pembroke Street. His father had made a rather startling career change and was now a self-employed chiropodist, and his brother and future business partner Gilbert (14) was now himself a pupil architect.

In 1892 Nathaniel was admitted as a Member of the Society of Architects. He commenced independent practice in Oxford in 1899, working at first from his parents’ home at 51 Rectory Road. At the time of the 1901 census Nathaniel (35), described as an Architect (Manager), was still living at home with his family, including his brother Gilbert Andrew Harrison (24). Gilbert, who had trained under Harry Wilkinson Moore and was now described as an architect's assistant, commenced independent practice as an architect in Oxford in 1903 and was in partnership with his brother. .

In 1903 Nathaniel was appointed the architect to St John's College, and served as “surveyor to the North Oxford building estate”. Most of this estate had already been created, but he did lay out Bainton Road, and he designed many houses in north Oxford (see list of his works below). By 1909 he had also been appointed architect to The Queen's College.

In 1905 he designed an extension to Headington Quarry Infant School, and by 1906 he had moved to Headington and was the head of the household at Highlands in Old Road, where he was to remain for the rest of his life. (This house is now numbered 57 Old Road, but until 1930 it was numbered 13 Old Road; then until 1947 it was 23 Old Road.) Originally in St Andrew's parish, it was transferred to Highfield parish when All Saints' Church opened in 1910.

On 2 December 1907 Nathaniel William Harrison was admitted as a Fellow of the Royal Institute of British Architects.

In 1909 Nathaniel William Harrison married Jeanie Watt Fulton. Born in Fenwick, Kilmarnock on 22 August 1880, she was the sister of James Black Fulton, F.R.I.B.A. They had four children, all born at 57 Old Road:

• Janet Frances Harrison (baptised at All Saints Church, Headington on 11 December 1910)
• Kathleen Mary Harrison (baptised at All Saints Church, Headington on 16 November 1912)
• Ronald Nathaniel Harrison (baptised at All Saints Church, Headington on 15 January 1916)
• James Fulton Harrison (baptised at All Saints Church, Headington on 25 September 1919)

On 21 July 1909 at St Giles' Church, Oxford, Nathaniel's younger brother Gilbert Andrew Harrison, described as an architect, married Ellen Eliza Anne Franklin of 4 Museum Road, Oxford, the daughter of the late Henry John Franklin. They moved into Campden House at the south-east end of Old Road, and their sons Gilbert Henry Franklin Harrison and Philip Andrew Harrison were baptised at Holy Trinity Church, Headington Quarry in 1914 and 1916 respectively.

In 1910 Thomas Rayson (who had studied under Harrison's brother-in-law James Black Fulton at the Brixton School of Building) came to Oxford as Nathaniel Harrison's pupil architect, and the 1911 census shows Rayson lodging with his employer's brother Hude Harrison in east Oxford. .

From 1910 to 1918 Nathaniel Harrison was in business partnership with his younger brother Gilbert, and the business, which was still run from his home at 57 Old Road, was listed in the commercial section for Headington in Kelly's Directory as “Harrison, N. W. & G.A. F.R.I.B.A., M.S.A.”.

In 1910 he made extensive alterations to The Rookery for Dr John Massie.

At the time of the 1911 census Harrison, described as an architect and employer, was living at 57 Old Road with his wife Jeanie and their first child, plus their 15-year-old servant girl. His father Nathaniel (75), now a retired chiropodist, and his mother Maria (71) were living with him in 1911, but by 1912 they had moved nearby to Whitecoate at 14 Bickerton Road.

In 1913–14 Harrison designed the nurses' home for the Warneford Hospital.

In 1914 he designed the present 39 St Andrew's Road for John Massie of the Rookery. The photograph below shows it shortly after it was built. It has since been extended, and was the home of Brian Aldiss from 1995 until his death in 2017).

In 1920 Harrison's father Nathaniel Harrison senior died at Bickerton Road, Headington at the age of 85 and his funeral was at St Cross Church on 30 November.

The 1921 shows Nathaniel Harrison (56) described as an architect and employer whose office was at 5 Turl Street living at Highlands (now 57 Old Road) with his wife Jeanie and their four children.

The brothers appear to have gone their separate ways and from 1926 until his death in 1944 Nathaniel had his own office at 5 Turl Street, while Gilbert relocated his practice to Maidenhead in Berkshire..

In 1926 Harrison's mother Maria Frances Harrison died at 14 Bickerton Road at the age of 87, and her funeral at St Cross Church on 8 July. Her effects came to just £5.

In 1937 Harrison designed the chancel of All Saints' Church in Lime Walk.

On 18 June 1944 Harrison's wife Jeanie Watt Harrison died at the age of 64 at the London Road Hospital (the former Headington Workhouse). She was cremated, and her ashes buried in Holywell Cemetery. Her effects came to £760.

Less than five months later on 7 November 1944 Nathaniel William Harrison himself died at the age of 79 at 57 Old Road, and his funeral was held at St Cross Church, Holywell, Oxford on 11 November. His effects came to £4,203 19s. 2d.

His brother and former partner Gilbert Andrew Harrison died at Sonning Common, Oxfordshire on 16 February 1962.

Some of the buildings designed by Nathaniel William Harrison

In Headington:

• 1905: Extension to Headington Quarry Infants’ School
• 1910: Extensive improvements and alterations to The Rookery to adapt it as the residence of Mr John Massie
• 1914: Gardener’s Cottage (now 39 St Andrew's Road: photograph below) for Mr Massie of The Rookery
• 1913–4: Addition of a nurses’ home to the Warneford Hospital
• 1935: Chancel of All Saints' Church in Lime Walk

For the University of Oxford and its colleges

• 1905: Renovation of Wycliffe Hall, 52  Banbury Road
• 1908: School of Forestry, Parks Road
• 1909: New chapel at St Hugh’s Hall, Norham Gardens
• 1909: The Queen’s College: Reconstruction of upper portion of cupola in Portland stone
• 1910: The Queen’s College: Renovation of clock tower in Clipsham stone
• 1914: Schools of Rural Economy, Parks Road
• 1927: Restoration of west front of the Library of The Queen's College
• 1930: Corpus Christi College barge (built in memory of the Revd Joseph Hooper Maude and his son Louis who died at the somme in 1916

New houses for St John's College on the North Oxford building estate

• Between 1905 and 1921: Nos. 1, 3, 9, 11, 15, 17, 25, 27, 29, 10, 16, 22, and 30 Charlbury Road
• In 1905 and 1910: Nos. 14 and 12 Linton Road
• 1909: No. 199 Woodstock Road
• Between 1911 and 1917: Nos. 5, 7, 2, 4, 8, 10, 12, 14, & 16 Chadlington Road
• 1915: No. 21 Northmoor Road
• 1932: No. 11 Belbroughton Road

In the rest of Oxford

• 1904: Cherwell Boat House
• 1905 and 1907: Improvements to house for Sir William Osler, Regius Professor of Medicine, at 13 Norham Gardens, including an addition to the garden front and a new bay on the south-west side
• 1907: Remodelling of St Giles’ Gate, 46 Banbury Road, for Dr Whitelock
• 1908: Alterations to the Old Bank, 92 High Street, including an extension of the front and a new larger entrance

• 1909: New building consisting of showrooms and cellarage for Messrs Eagleston & Son in St Clement’s near the Plain
• 1911: Alteration of the interior of George Street Congregational Church
• 1914: New building for Martyr Brothers hairdressers and William Baker china and furniture on corner of 1 & 3 Broad Street and 31 Cornmarket Street in consultation with Mr Payne Wyatt of London
• 1916: Restoration of the Oxford Institute at 29 & 30 St Aldate’s Street
• 1932: Restoration of the roof of Iffley Church

In the rest of Oxfordshire

• 1926–7: St Swithun’s Church, Merton, Oxfordshire: Tower Repairs (see Lambeth Palace Library record)

His brother Gilbert Andrew Harrison designed a number of buildings in Oxford, including the East Oxford Conservative Club, and residences for Professor W. M. Geldart and George R. Davis, Esq.