Christ Mocked, part of a series of paintings from the late 13th Century, was discovered at the property in the northern French town of Compiegne.
It is thought it could fetch up to â‚¬6m ($6.5m; Â£5.3m) at auction next month.
The woman had it valued believing it to be an old religious icon. Experts said there was “no disputing” its origin.
Tests were carried out on the artwork using infrared light to determine the similarities with works by the Italian painter Cimabue, also known as Cenni di Pepo.
“The painting was done by the same hand,” art expert Ã‰ric Turquin said, French newspaper Le Figaro reported.
It is believed to be part of a polyptych – a larger work of painted scenes divided into several panels – depicting Christ’s passion and crucifixion dating from 1280. …
In an interview with The Art Newspaper, Mr Turquin said that one of the clues to the painting’s origin lay in its panel.
“You can follow the tunnels made by the worms,” he said, referring to tracks in the panel made by wood-eating larvae similar to those found in other sections thought to be part of the same Cimabue artwork. “It’s the same poplar panel,” he added.
The painting, which the owner had hung above a hotplate in her kitchen, will be auctioned in France on 27 October.