Peter Greste, a former BBC correspondent who also worked for CNN International, was arrested in December 2013, alongside Al Jazeera's Mohamed Fahmy and Baher Mohamed after which they were all convicted for 10 years in jail for aiding terrorism and helping the outlawed Muslim Brotherhood organisation.
According to Reuters Mohamed Fahmy who holds Canadian citizenship will be released within days as well.
There's been no statement from Al Jazeera on Sunday evening, but Al Jazeera's acting director-general Mostefa Souag told BBC news that "We're pleased for Peter and his family that they are to be reunited. It has been an incredible and unjustifiable ordeal for them, and they have coped with incredible dignity."
Mostefa Souag said that Al Jazeera "will not rest until Baher Mohamed and Mohamed Fahmy also regain their freedom. The Egyptian authorities have it in their power to finish this properly today, and that is exactly what they must do."
On Sunday evening Al Jazeera America reported that the managing director of Al Jazeera English, Al Anstey said he was "relieved Peter Greste was freed and on his way home to be reunited with his family, but we've got to focus that Baher Mohamed and Mohamed Fahmy are still behind bars, and seven of their colleagues that were sentenced to ten years in absentia are still sentenced today."
UPDATE 22:51 - In a press statement received at 22:51 Al Jazeera says "that the campaign to free its journalists in Egypt will not end till all three have been released".
"Peter Greste is on his way out of the country after 400 days in detention, but Baher Mohamed and Mohamed Fahmy remain behind bars. All three have to be exonerated and the convictions against its Al Jazeera's other journalists tried in absentia also have to be lifted."
"Peter's integrity is not just intact, but has been further enhanced by the fortitude and sacrifice he has shown for his profession of informing the public," says Mostefa Souag, acting director-general of Al Jazeera Media Network in the statement.