The British Horseracing Authority also announced the meetings scheduled for Friday - including the third day of the St Leger meeting at Doncaster - have also been cancelled.
An announcement will be made on Friday regarding plans for Saturday, where the Leger at Doncaster is the showpiece event as the final British Classic of the season. Further details on plans throughout the period of mourning leading up to the Queen's funeral are expected in due course.
The Queen's final runner, Improvise, trained by Michael Bell and ridden by Benoit De La Sayette, was beaten a short head by Mount Kosciuszko in the Quick Ride by Quickslide Handicap over an extended mile at Epsom on Thursday.
The BHA said in a statement: "All of British Racing is in mourning today following the passing of Her Majesty The Queen.
"Her Majesty has been one of the greatest and most influential supporters in the history of horse racing. Her passion for racing and the racehorse shone brightly throughout her life, not only through her close involvement in breeding and racing horses, but in her roles as a patron of The Jockey Club and Thoroughbred Breeders Association, and as the figurehead of Royal Ascot.
"From her first-ever winner Monaveen, through stars such as Carrozza and Highclere, to the unforgettable Estimate, Her Majesty The Queen has helped to shape the breed and contributed to moments on the track that will go down in sporting folklore.
"It is right, therefore, that all racing is suspended for today and tomorrow as we begin to grieve Her Majesty's passing and remember her extraordinary life and contribution to our sport and our nation."
BHA chair Joe Saumarez Smith said: "The BHA extends our heartfelt condolences to the Royal Family and all those affected by this sad news.
"Racing owes an incalculable debt of gratitude, not only for Her Majesty's dedication and commitment to the sport, but for her public advocacy of it, something that doubtless has driven the sport's popularity and attracted a great number of fans.
Sandy Dudgeon, senior steward of The Jockey Club, said: "I would like to extend our heartfelt condolences to His Royal Highness The Prince of Wales, other members of the Royal Family and all those affected by the death of Her Majesty The Queen.
"Her Majesty's optimism about our future and her fortitude in the face of adversity was an example to us all. She was such a wonderful supporter of the sport of horseracing throughout her life, including as our Patron, and we will feel her loss most deeply indeed."
Elizabeth II, 96, was the nation's longest-reigning monarch, serving as head of state for more than 70 years.
The Prince of Wales is now King, having acceded to the throne immediately on the death of his mother.
In a statement, the Palace said: "The Queen died peacefully at Balmoral this afternoon. The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow."