In December 1989, he transferred to English team Chelsea, where he played for eight seasons and was voted player of the year for the club in 1995. He scored his only goal for the club against Southampton in April 1994. Whilst at Chelsea he played in the 1994 FA Cup Final. Chelsea won the 1996–97 FA Cup; in the fifth round against Leicester City FC at Stamford Bridge, Johnsen went down in the penalty area in the final minutes of extra time and referee Mike Reed awarded a penalty to Chelsea. The penalty was converted by Frank Leboeuf and secured a 1–0 win for Chelsea. It was considered by The Guardian's Scott Murray as one of the six worst referee decisions ever. Johnsen was left out of the squad for the final but played in the semi-final against Wimbledon. Shortly after this he returned to his native Norway where he played for Rosenborg and finally Strømsgodset before retiring in June 1999.