The house takes its current name from Philip Fenton, a merchant who traded from Riga on the Baltic coast and bought the property in 1793. In the 19th century he ordered the remodelling that shaped much of what visitors see today: alterations to the interiors and roof, the addition of the ornate portico and pediment over the entrance, new window frames and glazing. The balustraded parapets on the sides of the building date from the 18th century. The original staircases, with their twisted balusters, survived the remodelling. Main rooms retain their original panelling, corner cupboards, and decoratively carved marble fireplaces. The house passed through several more owners before reaching Lady Binning, its last private resident.

Upstairs, Fenton House holds the Benton Fletcher collection of early keyboard instruments — harpsichords, spinets, virginals, clavichords, and early pianos gathered by Major George Henry Benton Fletcher and donated to the National Trust in the 1930s. What makes this collection unusual is that the instruments are not merely displayed; during operational hours, musicians sometimes play them for visitors. A harpsichord built in 1612, a spinet from the 1730s, instruments that predated the modern piano entirely and produced sounds that concert halls no longer hear — these are still sounding, still in use, maintained as working objects rather than relics. The chance to hear one is not guaranteed, but the possibility is part of what makes Fenton House a different kind of visit.

Among the paintings at Fenton House are portraits of King William IV and Dorothea Jordan, the Irish actress who was his mistress for twenty years and bore him ten illegitimate children before he ended the relationship to marry a royal. The house also holds portraits of two of their sons, Lord Frederick FitzClarence and Lord Adolphus FitzClarence, and of William IV's brother George IV. The presence of this family grouping in a National Trust property — a king, his long-term mistress, their children — is quietly remarkable. William IV eventually became king in 1830. Dorothea Jordan died in poverty in France in 1816, never having received adequate financial support after the separation.

Hampstead's elevation above the rest of London gives Fenton House a particular relationship with the city below. The heath that stretches to the south and east has been common land for centuries, protecting the view across London's skyline. The walled garden, large enough to feel genuinely rural within the confines of the capital, contains the old orchard where the 30 varieties of apple were already well-established by the time of the National Trust's acquisition. In spring, the blossom fills the walled enclosure; in autumn, the apples are harvested. The house sits at the end of Holly Hill, in one of the few parts of London where it is still possible to hear birdsong without traffic as background noise.