Mr Gorbachev’s death at the age of 91 has inspired an outpouring of tributes from world leaders.
Many made reference to the timing of his death during the worst period of relations between Russia and the West since the end of the Cold War.
In a Twitter post, Mr Johnson said he was “saddened” to hear of Mr Gorbachev’s death, at a “time of Putin’s aggression in Ukraine”.
“I’m saddened to hear of the death of Gorbachev,” Mr Johnson said.
“I always admired the courage and integrity he showed in bringing the Cold War to a peaceful conclusion.
“In a time of Putin’s aggression in Ukraine, his tireless commitment to opening up Soviet society remains an example to us all.”
Labour leader Sir Keir Starmer said Mr Gorbachev was “one of the great figures” of last century who will “forever be remembered”.
In a tweet, he said: “One of the great figures of the 20th Century, Mikhail Gorbachev’s pursuit of reform forged a path for diplomacy over conflict.
“He will forever be remembered as the last leader of the Soviet Union who had the courage and conviction to end the Cold War.”
Irish premier Micheal Martin said: “I am deeply saddened to hear of the passing of Mikhail Gorbachev, one of the most significant political figures of the late 20th century.
“At a time when the threat to the world of nuclear destruction was very real, he saw the urgent need for rapprochement with the West and for greater openness and reform – glasnost and perestroika – in the then Soviet Union.
“His leadership helped to end the arms race between the East and West, end the Cold War and bring down the Iron Curtain that had divided Europe since the Second World War.”
The president of the European Commission praised the late politician’s legacy as “one we will not forget”.
In a Twitter post, Ursula von der Leyen said: “He played a crucial role to end the Cold War and bring down the Iron Curtain.
“It opened the way for a free Europe.
“This legacy is one we will not forget. RIP Mikhail Gorbachev.”
Former US secretary of state Henry Kissinger said Mr Gorbachev “performed great services” but was “not able to implement all of his visions”, telling BBC’s Newsnight: “The people of eastern Europe and the German people, and in the end the Russian people, owe him a great debt of gratitude for the inspiration, for the courage in coming forward with these ideas of freedom.”
Mr Kissinger, after again acknowledging Mr Gorbachev was unable able to implement his full vision, added: “He will still be remembered in history as a man who started historic transformations that were to the benefit of mankind and to the Russian people.”