She said the missile attacks had been aimed at deterring President Bashar al-Assad's further use of chemical weapons and were not an attempt to topple the Syrian government.
"This collective action sends a clear message that the global community will not stand by and tolerate the use of chemical weapons", May said at a press conference, calling the military action "right and legal".
The shadow of the 2003 invasion of Iraq still lingers in the corridors of Britain's parliament, when MPs backed then-prime minister Tony Blair in joining United States military action.
Lawmakers backed action in Iraq in 2014, and again in Syria in 2015, strictly limiting strikes in both countries to targets of the Islamic State jihadist group.
Over 100 missiles were fired on the morning of Saturday, April 14, targeting what representatives of coalition forces called chemical weapons sites in retaliation for an earlier poison gas attack.
Earlier Saturday, British Prime Minister Theresa May said that she has authorised the United Kingdom armed forces to conduct "coordinated and targeted strikes" in response to alleged chemical weapons attack in the Syrian town of Douma earlier this month.
"Britain should be playing a leadership role to bring about a ceasefire in the conflict, not taking instructions from Washington and putting British military personnel in harm's way", Corbyn said.
When asked if Syria's Assad could remain leader as long as he refrained from further use of chemical weapons, May said: "This was about, as I have said and you have recognized, this was specifically about the use of chemical weapons".
US President Donald Trump confirmed "precision strikes" had been ordered on targets associated with the Syrian government's chemical weapons programme.More news: Man Gets Three Life Sentences for Raping Women in Church
Scottish First Minister Nicola Sturgeon said Syria's use of chemical weapons could not be tolerated but questioned whether the strikes would halt their use or contribute to ending the civil war.
May said intelligence and open source accounts indicated that the regime was behind the attack in Douma last Saturday.
It returns from its break on Monday, when May will face MPs' questions on the strikes. The strikes at 0100 GMT were 15 miles (24 kilometres) west of Homs.
May held an emergency cabinet meeting to discuss possible action on Thursday and there had been calls for the British parliament to be consulted before any air strikes.
"There is also the question as to how this use of force will be linked and subordinated to strategies for bringing the fighting in Syria to a rapid end and for resetting relations between the West and Russian Federation", he said in the commentary.
"We can not tolerate the normalisation of the use of chemical weapons", he said in a statement.
By launching strikes without prior approval from parliament, May dispensed with a non-binding constitutional convention dating back to the 2003 invasion of Iraq.
May's office said she had spoken to the Crown Prince of Saudi Arabia, Mohammed bin Salman, Turkish President Tayyip Erdogan, German Chancellor Angela Merkel and the prime ministers of Italy, Australia and Canada about the strikes.