Alexandrani, who was arrested in November 2015, was accused of publishing military secrets and belonging to the banned Muslim Brotherhood, his lawyer Tarek Abdel Aal told AFP Tuesday.
He was also accused of spreading information that could harm national security outside the country in interviews with the media and in articles, his lawyer added. Abdel Aal said they will appeal the verdict.
Jailed Egyptian journalist to be awarded UNESCO press freedom prize
Alexandrani had been in pretrial detention for two and a half years since his arrest in the Red Sea resort of Hurghada after he returned from a work trip in Berlin.
An expert on militant movements in North Sinai, where security forces are fighting an insurgency led by the Islamic State group, Alexandrani had been to Germany to deliver lectures on the political situation in Egypt, his wife Khadija Gaafar had said at the time.
Egypt puts prominent critical of President Sisi on terrorism list
Alexandrani was also known for his anti-regime writings and for criticising the military's role in politics, and was a contributor to publications including the French online magazine Orient XXI, which confirmed his sentencing on Twitter.
Co-defendant Walid Mohareb was also sentenced to 10 years in prison in the same trial, which included 18 others who were being tried in absentia, Abdel Aal said.
The verdict "exemplifies the government's vicious retaliation against journalists who report on sensitive issues," Human Rights Watch Middle East director Sarah Leah Whitson said in an emailed statement.
"It's also a reminder that the government seeks to keep army abuses of Sinai residents away from media scrutiny," she said.
Human rights groups accuse President Abdel Fattah alSisi of installing a repressive regime that had led a crackdown against militants, which later expanded and targeted wider dissent.
Sisi was elected a year after he led the July 2013 military overthrew of his predecessor, Mohamed Morsi, amid mass protests against him.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ