Swedish defender Johansson joined F.C. Copenhagen in January 2016 and has established himself as vital player in both the domestic and European tournaments.
Manager Ståle Solbakken said: "Erik is a great and modern footballer. He has developed into a leader and has become one of the captains in the squad. He has performed at an international level for a longer period and has retired from the national team to be fully committed to FCK. He is in many ways a spectacular player.
"We expect Mathias Zanka to leave in the summer and with this extension, we have the foundation to build a new strong central defence around Erik."
Johansson said: "I love to live in this city and love playing for this club. That was the most important thing for me. We have experienced massive things on the pitch and I look forward to being part of FCK in the future."
