Writing in Newsweek, Schama, an expert on US history, lambasted Downton's improbable storylines and historical inaccuracies.
The attack comes just days after Downton Abbey, currently airing its second series in the US, was awarded a Golden Globe for Best TV Drama, Mini-Series or Motion Picture.
And while Schama has been busy criticising Downton, claiming "history's meant to be a bummer, not a stroll down memory lane", according to The Sun, US film execs are said to have been clambering to speak to the show's writer Julian Fellowes about a Downton Abbey film at the Golden Globes after-party.
Historian Simon Schama
Mr Schama might be fighting a losing battle. Downton Abbey remains the most popular British drama on US TV, regularly attracting more than four million viewers - significantly more than homegrown shows, including Mad Men or Game Of Thrones.
Schama isn't the first historian to make battle with the ITV period drama. In December, historian Jennifer Newby criticised Oscar-winner Julian Fellowes for his portrayal of servants in the country house drama, for looking too clean and acting far too familiarly with their employers. Plus, in the first season, sharp-eyed viewers spotted TV aerials and double yellow lines.