"Entirely the right thing to do".
The RAF joined U.S. and French jets in targeting Syrian bases this weekend, following a suspected chemical weapons attack in the rebel-held town of Douma that left scores of civilians dead.
"There is no proposal on the table for further attacks because so far, thank heavens, the Assad regime has not been so foolish to launch another chemical weapons attack", Johnson said.
British warplanes took part in the strikes, which destroyed sites suspected of hosting chemical weapons development and storage facilities.
"The erosion of that taboo that has been in place for 100 years has gone too far under Bashar al-Assad, and it was time that we said no".
Speaking on the Andrew Marr Show, the foreign secretary said the primary goal of taking action was "to say no to the use of barbaric weapons".
Prime Minister Theresa May is set to face British lawmakers to explain her decision to launch airstrikes against Syria without a vote in Parliament.
"We may not end the barbarism - but we are telling the world that there is one type of barbarism that is banned and that deserves to be banned".
Mr Johnson said Mrs May will be making a statement in the House of Commons on Monday and it will give parliamentarians a chance to hold the executive to account.
"Let me be absolutely clear: we have acted because it is in our national interest to do so".
Downing Street last night published its legal position on the airstrikes, arguing that there was "no practicable alternative to the use of force", and justifying the bombing on humanitarian grounds.
He also did not rule out further attacks against Syria if the Assad regime continued the alleged use of chemical weapons.