The government says it will seek an emergency parliamentary debate on the airstrikes Monday, though that is unlikely to satisfy angry opposition lawmakers.
"Entirely the right thing to do".
Sites near Damascus and Homs were hit by the United Kingdom, the USA and France in response to an alleged chemical attack on the town of Douma on 7 April.
"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.
The Foreign Secretary said Saturday's military action was necessary to show Syrian President Bashar al-Assad that the use of chemical weapons would not be tolerated.
"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" and I think it was totally, therefore, the right thing to do".
Yesterday Prime Minister Theresa May insisted the military action was "legal" and defended the decision to go ahead without securing the backing of Parliament.
"And we can not wait to alleviate further humanitarian suffering caused by chemical weapons attacks".
Addressing the Commons, Mrs May will set out her justifications for the decision - arguing it was taken on humanitarian grounds.
"We know what's in the Russian playbook, kompromat type material, we're all prepared for that", an intelligence source told the paper.
"We are confident in our own assessment that the Syrian regime was highly likely responsible for this attack and that its persistent pattern of behaviour meant that it was highly likely to continue using chemical weapons".