Johnson praised Donald Trump for showing “a resolve and willingness that has been sadly missing in the last few years”.
The US battered the Al Shayrat airbase in Southeastern Homs in retaliation to a chemical weapons attack in which at least 80 people died horrific deaths.
Washington warned Syria more military strikes could follow if they continue to launch chemical attacks, but would prefer a diplomatic solution.
Johnson said: “We cannot miss this moment. It is time for Putin to face the truth about the tyrant he is still propping up.”
And the Foreign Secretary was adamant critics “carping and using the death of civilians in a gas attack to fire off personal insults” were only emboldening the Russians and Assad.
Alex Salmond claimed the Foreign Secretary is in “deep political trouble” after pulling out of a meeting with Russia, in the wake of Trump’s Syrian intervention.
Johnson responded: “I am focussed on working with the US and getting the G7 behind the goal of ending this war and rebuilding Syria – one Rex Tillerson will deliver for the whole of the G7 to Russia.”
Russia has responded with fury, claiming the US is undermining Putin’s strategic efforts in the country.
Speaking to The Sun, Johnson added: “There is no doubt that the US action is a game changer in Syria.
“We need to make it clear to Putin that the time to back Assad has gone. By continuing to support a man who gasses his own people he is damaging Russia further in the eyes of the world.
“He must now understand that Assad is now toxic in every sense. He is poisoning the innocent people of Syria with weapons that were banned 100 years ago. And he is poisoning the reputation of Russia.”
A joint command centre of Russia, Iran and Islamist militant group Hezbollah warned America they would not allow further attacks on the Syrian regime.
The military chiefs declared in a joint statement: “From now on we will respond with force to any breach of red lines and America knows our ability to respond well.”