The British-Iranian aid worker has also been banned from leaving the country for a year, her lawyer Hojjat Kermani told Emtedad news website on Monday.
"Nazanin Zaghari was sentenced to one year in prison and one year ban from leaving the country on charges of propaganda against the Islamic Republic," Mr Kermani told the website.
Mr Kermani said she received the second sentence on a charge of spreading "propaganda against the system" for participating in a protest in front of the Iranian Embassy in London in 2009.
The lawyer said he would appeal the new sentence within 21 days under Iranian law.
Mrs Zaghari-Ratcliffe family and her employer, the charity Thomson Reuters, deny the charges.
Her husband Richard Ratcliffe told the BBC that the court's decision was a bad sign and "clearly a negotiating tactic" by the Iranian authorities who are currently in middle of discussions to restore the country's nuclear deal.
Mr Ratcliffe told the broadcaster she had not been summoned to prison at this point.
Prime Minister Boris Johnson said on Monday that he thought the sentencing was "wrong".
"I don't think it's right at all that Nazanin should be sentenced to any more time in jail. I think that it was wrong,” he said.
"I think it's wrong that she's there in the first place and we'll be working very hard to secure her release from Iran."
He added that the "government will not stop" and will "redouble our efforts" to fight for Mrs Zaghari-Ratcliffe's release.
Foreign Secretary Dominic Raab called the detention of Mrs Zaghari-Ratcliffe for a further year "totally inhumane and wholly unjustified".
“We continue to call on Iran to release Nazanin immediately so she can return to her family in the UK. We continue to do all we can to support her,” he tweeted.
Mrs Zaghari-Ratcliffe’s MP Tulip Siddiq, who represents Hampstead and Kilburn, wrote on Twitter: "Thank you for all the messages regarding Nazanin.
“Absolutely devastating news and shocking that her husband was only just notified. Another abusive use of her as a bargaining chip. I'm speaking to the family & will update when I know more."
The 42-year-old mother has been separated from her daughter and husband for almost five years after she was arrested at Tehran’s Imam Khomeini airport.
She has always denied all claims.
Mrs Zaghari-Ratcliffe completed her full sentence in March and finished the latter part of it under house arrest due to the coronavirus crisis.
However, on the day she had her ankle tag removed, she was told she would be summoned back to court on a new charge of propaganda against Iran.