Adly Mansour has told Peter Greste's family that he will push to expedite the case against the Australian reporter.
"I would like to assure you in my capacity as president of Egypt, that I will spare no effort to work towards the speedy resolution of the case, in a fashion consistent with the law and that guarantees the reunion of the family in the near future," Mansour wrote in the letter, seen by The Associated Press on Tuesday.
It's unclear if the letter directly mentions Egyptian-Canadian Mohamed Fahmy or Egyptian Baher Mohamed, who were arrested along with Greste on Dec. 29 in Cairo.
The three journalists are accused of endangering national security and aiding a terrorist organization along with 17 others.
Authorities accuse Al-Jazeera of being a platform for ousted Islamist president Mohammed Morsi's supporters and his Muslim Brotherhood group. The network denies that and says the journalists were just doing their jobs.
Greste, Fahmy and Mohamed all appeared in an Egyptian court earlier this month. They have all pleaded not guilty.
Their trial marks the first time Egypt has prosecuted journalists on terrorism-related charges.
It comes amid an extensive crackdown on some secular dissidents and Brotherhood supporters.
The trial, which was adjourned on March 5, resumes March 24.
Fahmy's family moved to Canada in 1991. He lived in Montreal and Vancouver for years before eventually moving abroad for work which included covering stories for the New York Times and CNN.
The Department of Foreign Affairs has said senior Canadian officials have raised Fahmy's case with Egyptian authorities and have requested a fair and expeditious trial.
Fahmy's family has also noted that while consular staff in Cairo have been extremely helpful, officials have indicated the 40-year-old's dual citizenship limits how much they can do.