The opening is marked by the 91-year-old Queen's speech, traditionally read out by the monarch toset out the government's legislative agenda for the year.
The event had already been scaled down as a result of the snap general election, with the Queen set to forego the traditional robes and finery.
In a briefing, the Prime Minister's official spokesperson declined to confirm that the Queen's Speech would still be held on June 19 as previously announced, saying that the new Leader of the Commons, Andrea Leadsom, will soon be releasing a statement on the date.
"We'll have to look at the Queen's Speech and what we have to get through. It has to be voted on in Parliament in a week's time; it's a matter of practicality. There may be things that we simply can't put in. That will happen. That will be going on as we speak. We will try to carry as much of the House with us as we can," he said.
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The delay in the Parliament opening is believed to be mainly the result of ongoing talks between May and the Democratic Unionist Party (DUP) - whose 10 MPs are crucial to her new minority government after last week's general election threw up a hung Parliament.
The reason behind the delay would indicate that the British Prime Minister is set to make changes to the Queen's Speech, which is prepared by the government of the day.
This was seen as inevitable in order to water down some of the proposals the Conservatives now feel have proved unpopular with the electorate as well as taking into account the demands of the DUP to get legislation passed through the House of Commons.
The ongoing negotiations with the DUP will begin to take official form with a meeting at Downing Street between May and DUP leader Arlene Foster on Tuesday.
Meanwhile, May was holding her first meeting of her new political Cabinet with a full-fledged Cabinet meeting scheduled tomorrow.
Later today, she is set to face the Conservative party's 1922 Committee of backbench MPs, who will question her on various aspects of her leadership, including the Brexit negotiations set to begin later this month.
With 318 seats, the Tories are left dependent on the DUP to shore up its ranks to go past the 326-MP majority required in Parliament.
Labour party leader Jeremy Corbyn, who fared far better than forecast in the polls winning 262 seats, has accused May of "squatting" in No.
10 Downing Street and has said his party is ready to take the lead to form a government or face the electorate in another election to win a bigger mandate.