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.”
Former US secretary of state Henry Kissinger said 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.”
Former US Secretary of State James A Baker III, who dealt regularly with Gorbachev for years on issues like the Berlin Wall and NATO, called the former Soviet leader a “giant.”
“History will remember Mikhail Gorbachev as a giant who steered his great nation towards democracy,” Mr Baker said.
“He played the critical role in a peaceful conclusion of the Cold War by his decision against using force to hold the empire together,” the US official added. “I found him to be an honest broker and could count on his word despite domestic pressure in Moscow. The free world misses him greatly.”
Ursula von der Leyen, president of the European Commission, called Gorbachev “a trusted and respected leader.”
“He played a crucial role to end the Cold War and bring down the Iron Curtain,” she wrote on Twitter on Tuesday. “It opened the way for a free Europe. This legacy is one we will not forget.”
UN Secretary-General Antonio Gueterres described Gorbachev as a “one-of-a-kind statesmen”.
He said: “I was deeply saddened to learn of the passing of Mikhail Gorbachev, a one-of-a kind statesman who changed the course of history. He did more than any other individual to bring about the peaceful end of the Cold War.
“The world has lost a towering global leader, committed multilateralist, and tireless advocate for peace.”
Gorbachev died on Tuesday “after a serious and long illness” in a Moscow hospital.