The Long Gallery, running along the upper floor of the west side of the house, was completed by the late 16th century, though much of its interior reflects later change. Panelling and fireplaces from the 17th century were followed by the installation of large bookcases in the 1740s, when Cuthbert Constable transformed the space into a library to house his growing collection. 

By the 18th century, the Gallery had become a place not only for books but for study and experiment, with scientific instruments and furnishings reflecting a growing interest in learning. In the 19th century, the room was richly redecorated with plasterwork, textiles and furniture, giving it the character seen today. 

It also became a social space, used for gatherings, music and entertainment. These layers of use remain visible, creating a room that reflects both intellectual life and the social world of the house.