The American journalist was arrested in March during a work trip to the city of Yekaterinburg, almost 2,000km east of Moscow. He is the first US journalist since the Soviet era to be held on espionage charges in Russia.
An order that authorised keeping Gershkovich in jail before trial was set to expire on August 30. The Moscow City Court extended the custody order on Thursday by three months, drawing objections from US government officials and the Journal.
The court's website on Saturday showed that Gershkovich's defence team had filed an appeal. The court in June rejected his appeal of the earlier ruling to keep him behind bars until the end of August.
Journalists gathered outside the court on Thursday were not allowed to witness the proceedings. Russian state agency Tass said the hearing hearing was held behind closed doors because details of the criminal case are classified.
Russia's main internal security agency, the Federal Security Service, has alleged that Gershkovich, 31, "acting on the instructions of the American side, collected information constituting a state secret about the activities of one of the enterprises of the Russian military-industrial complex."
Gershkovich and his employer deny the allegations, and the US government in April declared him to be wrongfully detained. Russian authorities haven't detailed what, if any, evidence they have gathered to support the espionage charges.
The Wall Street Journal released a statement on Thursday referencing Gershkovich's "improper" detention "for doing his job as a journalist."
"The baseless accusations against him are categorically false, and we continue to push for his immediate release. Journalism is not a crime," the statement said.
Earlier this month, US Ambassador to Russia Lynne Tracy made her third visit to the jailed Gershkovich and reported that he appeared to be in good health despite his challenging circumstances. He is being held at Moscow's Lefortovo prison, notorious for its harsh conditions.
Gershkovich is the first American reporter to face espionage charges in Russia since September 1986, when the KGB arrested Nicholas Daniloff, a Moscow correspondent for US News and World Report.
Analysts have pointed out that Moscow may be using jailed Americans as bargaining chips after US-Russian tensions soared over the Kremlin's military operation in Ukraine. At least two US citizens arrested in Russia in recent years - including WNBA star Brittney Griner - were exchanged for Russians jailed in the US.
The Russian Foreign Ministry has previously said it would consider a swap for Gershkovich only in the event of a verdict in his trial. In Russia, espionage trials can last for more than a year.
