The announcement, made in parliament by speaker John Bercow, confirms that Ms May can begin divorce talks at any time, although her spokesman hinted on Monday that any such decision was likely to come towards the end of the month rather than in the coming days.
The European Union (Notification of Withdrawal) Bill was signed by the Queen today after it was cleared by both chambers of the British Parliament earlier this week, reported the Independent.
"I have to notify the House in accordance with the Royal Assent Act 1967 that her Majesty has signified her royal assent to the following acts... European Union (Notification of Withdrawal) Act 2017," Commons Speaker John Bercow told lawmakers during a session of the house.
The bill gives Ms May the legal authority to trigger Article 50 of the Lisbon Treaty, the laid down procedure within the EU for a member state wishing to leave.
Once Article 50 is triggered, it kickstarts a two-year process for negotiating a new relationship between both sides.
The Prime Minister is now free to trigger the exit clause, but is not expected to do so until as late as March 29, the newspaper reported.
A Downing Street spokesman said: "The legislation has been passed unamended, we are pleased that's the case. The legislation has got Royal Assent and we look forward to triggering negotiations by the end of March."
Senior figures in Brussels have warned that the timetable will be too tight if May triggers Article 50 in the last week of March, said the report.