Mary Beard is the biggest name yet to support the appeal by High Storrs School in Ecclesall, which is believed to be the city's only state school still teaching the subjects.
The Cambridge University classics professor, who is famed for her documentaries and books about Roman civilisation, said: "I am right behind any efforts to keep classical subjects in schools."
Staff at High Storrs are seeking to raise £100,000 to ensure they can continue to teach Latin and classics and prevent them becoming the preserve of public school students.
They say a combination of small class sizes and school funding cuts mean the subjects could be threatened there if the money cannot be raised.
Teacher Gina Johnson said she was delighted by Mary Beard's support, which she hoped would raise the campaign's profile, though she did not believe the scholar had contributed financially.
She said around £9,500 had been raised since the crowdfunding campaign went live at the end of September.
That sum is set to be bolstered considerably by a 'very significant' donation from Sheffield businessmen Sir Andrew Cook and John Hancock, who both studied Latin at the school during the 1960s.
"It's great to have Mary Beard backing our campaign, because she's the country's most prominent classicist," said Ms Johnson.
"We're very happy with how the campaign is going so far. As well as raising enough to secure Latin and classics classes in the short-term at least, it's helped raise the profile of the subjects and generated more interest from potential sixth form students."
* You can donate at www.justgiving.com/crowdfunding/save-classics.