The pontiff's announced he'll meet with Patriarch Kirill in Cuba next week before his trip to Mexico.
It will be the first such meeting since the Western and Eastern branches of Christianity split in the 11th Century.
The Vatican said the two leaders would sign a joint declaration following a meeting at Havana Airport.
The meeting marked "an important stage in relations between the two churches," a statement said.
It asked Christians to pray "fervently for God to bless this meeting" so it would "bear good fruits".
Pope Francis has been keen to secure better relations between the different branches of Christianity since taking up the role in 2013.
The meeting will pave the way for direct ties between the Catholic and Russian Church, which is the largest in the Orthodoxy.
Vatican spokesman Fr Federico Lombardi told reporters: "After centuries it is the first time that the pope will meet with the head of the Russian Orthodox Church. It is an event of extraordinary importance."
A statement from the clergyman added: "The Holy See and the Patriarchate of Moscow are pleased to announce that, by the grace of God, His Holiness Pope Francis and His Holiness Patriarch Kirill of Moscow and All Russia will meet on February 12 next.
"Their meeting will take place in Cuba, where the Pope will make a stop on his way to Mexico, and where the Patriarch will be on an official visit. It will include a personal conversation at Havana's José Martà International Airport, and will conclude with the signing of a joint declaration.
"This meeting of the Primates of the Catholic Church and the Russian Orthodox Church, after a long preparation, will be the first in history and will mark an important stage in relations between the two Churches. The Holy See and the Moscow Patriarchate hope that it will also be a sign of hope for all people of good will.
"They invite all Christians to pray fervently for God to bless this meeting, that it may bear good fruits."
