But she avoided answering questions on whether parliament would be consulted on any further strikes and ignored demands by Corbyn for a War Powers Act to limit the government's power to launch military action.
She went on to list the evidence that Syrian regime had to be behind the attack, including witness and NGO reports, as well as the fact that the military hardware required for such an attack could not have come from "Islamic State" terrorists or other Syrian rebels.
"I'm absolutely clear that it is parliament's responsibility to hold me to account for such decisions and parliament will do so", May told the House of Commons in a rowdy session.
Liberal Democrat leader Vincent Cable said he was also concern that May "made a grave mistake not bringing the case for military action to parliament", and like Corbyn, accused her of "riding on the coat-tails of an unpredictable U.S. president".
Johnson said May and her cabinet of top ministers had to move quickly on Syria, so could not risk recalling parliament from its holiday break, and added that there were plenty of examples of when a prime minister did not get its approval.
"The prime minister is accountable to this Parliament, not the whims of the USA president", Corbyn said.
"Seventy-five people, including young children, were killed in a horrific chemical attack", said May, calling the attack "a stain on our humanity". "We have done it because we believed it was the right thing to do", she said.
May will make a statement on the action to the House of Commons on Monday, but opposition lawmakers have lined up to call for a more meaningful debate and a possible retrospective vote on the action, which would severely test her position.
In Luxembourg, the foreign ministers of the 28 European Union countries called for a political breakthrough involving regional players to put Syria on track to a peaceful solution for its seven-year conflict.
But in a sign that the government feels under pressure, one lawmaker said on condition of anonymity that the party's whips, charged with maintaining voting discipline, had made clear that Conservatives should vote with the government.
Corbyn won approval for a debate on parliament's rights in regard to British military action on Tuesday, and parliament debated long into the evening on Monday on the government's strategy in Syria, particularly regarding civilians there. The joint statement comes amid worsening relations between the two countries and Moscow, after Washington and London launched coordinated strikes against Russia's ally Syria. May has emphasised that the strikes were "limited" to only target Damascus's chemical weapons programme.
"There's no more serious issue than the life-and-death matter of military action, and Parliament has the right to support or stop the government taking military action".
But she will be mindful of how military action can backfire. "That is what we have done and what we will continue to do", she concluded. Some 36 percent supported the strikes. "If not, she's the one that will take the blame".