Sir John Molesworth, the fourth Molesworth baronet, started the construction of Pencarrow in the 1760s, extending a large older house on the site, and it was completed after his death in 1766, by his son, the fifth baronet, also Sir John Molesworth. The architect was probably Robert Allanson. The initial remodelling of the house may have begun around 1730, as the Palladian style of the house was somewhat out of fashion by the 1760s and 1770s when much of the work was done. Another clue is that the symmetry of the south and east fa?ades is not matched by any symmetry in the interior plan, possibly because the layout of the building’s rooms inhibited the axial symmetry associated with the Palladian style.
The oldest parts of the house probably date from the late 17th or early 18th century, although there was earlier building on the site. The south and east fa?ades are stuccoed stone rubble and brick, while the north side is stone rubble. The west side is built of dressed slate stone with a moulded plinth. The roofs are slate with hipped ends on the south and east fronts.