Jason Rezaian, a dual US-Iranian citizen, is scheduled to go on trial at a Revolutionary Court on Tuesday.
His wife Yeganeh Salehi, who was arrested alongside him in July but later bailed, and a third person have also been summoned to appear in court.
It is not clear whether proceedings will be open to the public.
The Washington Post's executive editor, Martin Baron, denounced what he called the "contemptible prosecution" of Mr Rezaian, who has been allowed only a single meeting with his lawyer - in the presence of official translators - to prepare.
Iranian state media quoted an unnamed judiciary official as saying on Tuesday that Mr Rezaian and two others would appear in court for the first time next week.
The journalist's lawyer, Leila Ahsan, told the Associated Press that she had confirmed the news with the court.
She said the other two defendants were Ms Salehi, who was a reporter for the Abu Dhabi-based newspaper The National, and a freelance photographer who worked for foreign media who has not been named publicly.
It was not yet clear whether the trial would be open, she added. Revolutionary Courts, which hear cases involving state security, normally conduct hearings in closed session.
Mr Rezaian, who had been the Washington Post's Tehran bureau chief since 2012, was charged in December but the nature of the charges was only revealed in April.
At the time, Ms Ahsan said he had been accused of espionage for allegedly collecting confidential information about Iranian domestic and foreign policy and handing it to "hostile governments".
Mr Baron urged Iran to "belatedly demonstrate that it can act with openness and fairness".
"The serious criminal charges that Jason now faces in Iran's Revolutionary Court are not supported by a single fact," he said in a statement on Tuesday.
"The proceedings against him have been anything but fair and open - if they had been, Jason would never have been subjected to outrageous prison conditions, obstacles to selecting a lawyer, limited time to prepare a defence, and an inadequate window on the case that Iran plans to bring against him."
The US State Department has said the charges are "patently absurd" and President Barack Obama has urged Iran to release Mr Rezaian.
The trial of a Washington Post journalist detained in Iran for almost 10 months on charges that include "espionage" will begin next week.