The 4ft 4in x 3ft 6in (1.33 x 1.06m) oil on canvas was consigned to Dorotheum from an aristocratic collection where it had been since the mid-19th century. It had an upper estimate of €700,000. It was knocked down to a bidder in the saleroom on October 23 and will join a private Australian collection.
Like many of the 60 or so paintings attributed to Gentileschi, this work features a strong female subject, and is considered to have an autobiographical edge. Lucretia depicts a woman from Roman historical legend who killed herself after being raped by the son of a king.
The artist, whose legacy is dominated by her personal story, was raped by fellow artist Agostino Tassi and took part in his prosecution.
Her self-portrait as St Catherine of Alexandria (c.1615-17) was bought by the National Gallery in London for £3.6m this summer.