A sketch of a woman’s head by Charlotte Brontë, previously thought to be of another pupil drawn while the author was at boarding school in Brussels, has been identified as a self-portrait. The literary biographer Claire Harman said the drawing, which she suggests shows Brontë looking into a mirror, preceded the novel Jane Eyre, in which the protagonist also draws herself in a similar fashion.

The sketch dates from 1843, four years before Brontë published Jane Eyre, one of English literature’s great masterpieces, and when the young writer was suffering the agonies and insecurities of unrequited love.

So much of the novel was “autobiographical with fictionalisation”, Harman said. “There’s a passage when Jane [tries] to convince herself that she must ... not be deluded into thinking Mr Rochester liked her more than an employer would ... because she does not deserve his attention. She’s too poor, plain and disconnected. So she sits down and draws her self-portrait. She gets a mirror and makes her own portrait in order to convince herself of her own unattractiveness.”

“If Brontë actually tried to be realistic in a self-portrait, that might well have recurred in her mind when she was writing Jane Eyre, to put in a scene like that,” says Harman.

Noting the sketch’s awkward pose, with the hand “shoved under the chin”, Harman said: “It does look as if it’s been done in [front of] the mirror.”

The drawing was known to be by Brontë, not least because it was sketched on her school atlas. But it has remained unpublished until now, recorded without an image in the 1995 scholarly volume The Art of the Brontës as “possibly a sketch of a fellow pupil in Brussels”. It is owned by the Pierpont Morgan Library in New York.

Harman, who taught English at the universities of Manchester and Oxford, has included her discovery in her book, Charlotte Brontë: A Life, published this week. Brontë had adept draughtsmanship skills. At one time, she wanted to be an artist and was drawing and painting for up to nine hours a day.

Harman’s discovery is “massively significant” as there are only two other known lifetime portraits of Brontë. The writer was painfully self-conscious about her looks, and this portrait has been identified from descriptions of her unflattering features – a large nose, prominent brow, penetrating eyes and a mouth that twisted up to one side, hiding decayed teeth.

Harman said: “She must have thrown a lot of stuff away. This has survived ... because it was in a printed book.”

Brontë took the atlas on her visit to Brussels with her sister Emily. As mature students, they attended a high school for young women, mostly Belgian, and the older Brontë sisters kept to themselves. They went partly to polish up their language skills, but Charlotte became obsessed with Constantin Héger, the headmistress’s husband, and was unable to forget him when she left the school in 1844. Although he would not respond, she bombarded him with letters.

In one passage, Brontë wrote: “Day and night I find neither rest nor peace – if I sleep I have tormenting dreams in which I see you always severe, always saturnine and angry with me. Forgive me then monsieur if I take the step of writing to you again. How can I bear my life unless I make an effort to alleviate its sufferings?”

Commenting on the sketch’s significance, Harman said that readers yearn to know what a favourite author looked like: “If you love an author and their work, you have a strong empathy with them ... You want to be able to imagine them and commune mentally with them as a person.”

Despite the sketch’s small size – barely 1.5 inches high – its facial details resemble those in an 1850 image by George Richmond, now in the National Portrait Gallery, although the artist was known to flatter his sitters.

One other contemporary likeness was part of a group portrait painted by Charlotte’s brother Branwell. Ann Dinsdale, collections manager of the Brontë Parsonage Museum in Haworth, said any insight into how Charlotte saw herself is interesting. Although it is hard to prove conclusively, she added: “It does look very similar to the sitter in the Richmond portrait.”