Cameron will be joined by leaders of other political parties in thanking the Queen for her 63 years of service, as the 89-year-old monarch overtakes the record of her great-great-grandmother Queen Victoria on September 9.
Commonwealth Secretary-General Kamalesh Sharma paid an early tribute to the Queen, describing her as "all that is best in the Commonwealth".
"The Queen's personal commitment as Head of the Commonwealth is exemplary, and her devotion to advancing cooperation and understanding continues to inspire people of all ages Commonwealth-wide," he said in a statement.
"In congratulating Her Majesty on this historic occasion the Commonwealth joins with a fresh sense of common purpose, committed to advancing in practical ways the shared values and principles now set out in the Commonwealth Charter," he said.
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National leaders from Commonwealth realms around the world are also expected to add their own words of thanks, on a day of celebration that will begin on the Pacific island of Tuvalu and in Canada.
After Cameron's message from the House of Commons, attention will turn to Jamaica, Belize and the Caribbean island nations that have the Queen as their head of state, and to Canada, which has organised a half-hour musical tribute.
The pieces will include music from the year of the Queen's birth through to the present day.
The Queen is herself expected to make a rare speech when she opens a new railway line in the Borders area of Scotland tomorrow afternoon.
Buckingham Palace has calculated her total number of days on the throne until September 9 as 23,226 and 12 prime ministers who have served under her, the first being Winston Churchill and the latest being Cameron.
Born on April 21, 1926 in London, the Queen was christened Elizabeth Alexandra Mary of York and was known as young "Lilibet" to her family.
It seemed at the time unlikely that she would become Queen until her uncle, Edward VIII, abdicated in order to marry American divorcee Wallis Simpson.