"This is not about intervening in a civil war".
"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", she will add.
She stated the airstrike was "limited and targeted" created to minimize civilian casualties and bring down the chemical weapon capability in Syria, Reuters reported.
The Prime Minister has been speaking to Donald Trump and Emmanuel Macron over the past week to co-ordinate a response to the alleged chemical attack by President Assad's regime of Syrian civilians last weekend.
The Prime Minister will tell MPs on Monday that the strikes were in the national interest because the use of chemical weapons can not be normalised, including in the UK.
Mrs May will make the statement explaining why she ordered British cruise missile strikes and will then take questions from MPs.
"There is a wider question on the future political solution for Syria and that is a matter that we will continue to pursue in diplomatic and political channels with our worldwide partners and allies", May said. "Let these united actions send a clear message to the regime - the use of chemical weapons is categorically unacceptable and you will be held to account".
In her comments, May also alluded to a nerve agent attack in Britain last month on a former Russian spy and his daughter.
He said: "The goal of our actions tonight is to establish a strong deterrent against the production, spread, and use of chemical weapons".
"This is the first time as prime minister that I have had to take the decision to commit our armed forces in combat - and it is not a decision I have taken lightly", she said.
Syrian state TV said the army's air defences shot down 13 missiles.
The Prime Minister will tell parliament that United Kingdom air strikes in Syria were carried out to alleviate further suffering in the country.
Parliament is not due to reconvene until Monday, following its Easter recess.
A YouGov poll for The Times newspaper this week indicated that only a fifth of voters believed that Britain should launch attacks on Syrian military targets and more than two-fifths opposed action.
But they backed action in Iraq the following year, and again in Syria in 2015, strictly limiting strikes to targets of the Islamic State group. "The [Syrian] opposition does not operate helicopters or use barrel bombs".
"This legally questionable action risks escalating further.an already devastating conflict", he said, adding that May should have sought parliamentary approval.
Vince Cable, leader of the Liberal Democrats, said: "Riding the coattails of an erratic U.S. president is no substitute for a mandate from the House of Commons".