Syed and Christian leaving Walford
The pair, who play gay lovers Christian Clarke and Syed Masood, are being written out after Marc decided to leave the long-running BBC One soap.
He said: "I have had a brilliant time on EastEnders over the last three and a half years and made some amazing friends.
"During this time, I have been blessed with some incredible storylines and am especially pleased that the show has tackled and raised awareness of the sensitive subject matter of being a gay Muslim.
"As an actor you are always looking for new challenges and I feel that now is the right time to move on and explore different projects, perhaps returning to my roots in theatre."
Show bosses have remained tight-lipped about how the couple will leave the square.
John, who plays Christian, has also been seen as a member of the judging panel for the Andrew Lloyd Webber show Over The Rainbow.
He said: "I have had the time of my life at EastEnders - but I have always gone with my gut, and leaving at the same time as Marc felt like the only thing to do.
"It is the right end to the story and for Christian. But also, excitingly, the start of a whole new chapter for me."