Gregory employed two of the leading architects of Victorian England, Anthony Salvin and William Burn and consulted a third, Edward Blore, during its construction.

Its architecture, which combines elements of Jacobean and Elizabethan styles with Baroque decoration, makes it unique among England's Jacobethan houses.

[2] The original Harlaxton Manor was an ancient building in need of repair so Gregory did not move to the house, living at the nearby Hungerton Hall.

Unmarried, childless, with no interest in traditional country pursuits, and averse to socialising and entertaining, the building of Harlaxton, and the acquisition of architectural elements, paintings, furniture and glass to fit it out, became Gregory's all-consuming passion.

He travelled into all parts of Europe collecting objects of curiosity, useful or ornamental, for his projected palace, and he did not begin to build until he had accumulated money enough to complete his design.

He says that it is his amusement, as hunting or shooting or feasting may be the objects of other people and as the pursuit leads him into all parts of the world, and to mix with every variety of nation and character, besides engendering tastes."

In 1851 Gregory moved into the completed manor with a staff of fourteen servants including a butler, a house keeper, three footmen, seven domestic maids and two grooms.

Shortly thereafter, Harlaxton Bureau correspondents covered the death of Princess Diana and were subsequently recognized by the Indiana Society of Professional Journalists.

Exterior and interior shots have featured in The Ruling Class,[24] The Last Days of Patton,[25] The Lady and the Highwayman, The Haunting,[24] The Young Visiters[26] and The Secret Garden.

[27] Nicholas Antram, in his revised Lincolnshire volume of the Pevsner Buildings of England published in 2002, describes the approach to Harlaxton Manor as a "crescendo of effects".

[28] From the entrance gates on the A607, just outside of the village of Harlaxton, the drive descends into a valley before crossing a serpentine lake by way of a five-arch bridge.

[31] It continues past the stables before entering the Cour d'honneur through a second, double, gatehouse, described by Antram as a "pyrotechnic display".

[d][34] Salvin enhanced the drama of the entrance front by making the entry at basement level, the corresponding garden elevation behind opens directly onto a parterre.

[39] The main architectural style is that of an Elizabethan or Jacobethan prodigy house, such as nearby Burghley or Wollaton Hall in Nottinghamshire, although with notable European influences.

[41] Mark Girouard, in his 1979 study, The Victorian Country House, records that Gregory had visited "Bramshill, Hardwick, Hatfield, Knole, Burghley, Wollaton, Kirby Lonleat, Temple Newsam and the Oxford and Cambridge colleges " in pursuit of Elizabethan inspiration.

[42] Girouard notes that this blending continues "in varying proportions all through the house"[43] and suggests David Bryce, William Burn's chief assistant, as a possible source.

[34] The sources for all of these elements can be traced: the overall impression is of Burghley House; the pilasters are a direct lift from a 16th-century German architectural work, the Architectura by Wendel Dietterlin, a copy of which Gregory is known to have owned;[45] the oriel is from Hengrave Hall in Suffolk.

The reason for this is unclear, but the consensus among architectural historians is that disagreements of Gregory's future plans for the design and decoration of his house led to an estrangement.

[e][32] Antram considers the lodges and screen to be unlike anything else in England of that date, and comparable only to the work of John Vanbrugh at Blenheim Palace.

Jill Franklin, in her 1981 study, The Gentleman's Country House and its plan 1835-1914, writes of the unusual nature of the interior layout of Harlaxton.

Noting that there is no easy means of circulation, and that the entrance hall, the only public space at the front ground floor level, leads up via flights of stairs to two awkwardly placed landings, through which entrance is made into the main entertaining rooms of the house by concealed jib doors, she suggests that the house was always in fact designed for show, rather than for living; "a guided tour, with the visitor giving delighted cries of surprise as each door is flung open".

While there, and taking advantage of the cheap prices occasioned by the end of the Napoleonic Wars, he embarked on a spending spree purchasing, "panelling, chimneypieces, furniture and tapestries in great quantity".

[35] The wood carver William Gibbs Rogers, who visited the house in the 1860s when Gregory's collection was still intact, recorded his impressions; "marbles, jaspers, cabinets, porcelain of fabulous value, Buhl, rare sculptures, delicate carvings, furniture, tapestries, all in glorious and unreadable confusion".

The main inspiration for what Gregory called The Barons' Hall, is that at Audley End House in Essex, but the design and decoration has decidedly Baroque elements such as the "muscular atlantes" supporting the roof trusses.

[i][55] The chandelier is a later introduction, bought by Mrs Van Elst, when its transportation to the intended destination, a palace in Madrid, was interrupted by the Spanish Civil War.

[48] It appears to rise three full storeys in what Michael Hall, in his 2009 study, The Victorian Country House calls an, "astonishingly theatrical tour de force".

The decoration is entirely Baroque; "swagged curtains interlaced with thriving putti blowing trumpets and supporting huge scallop shells".

[5] An alternative theory is that Salvin, who is known to have visited Bavaria in 1835, brought back local German craftsmen to undertake the work,[36] but architectural historians favour the former suggestion.