Customers had difficulty accessing tickets due to the official website crashing, while sections of empty corporate seats at key events angered the public.
Football had the most seats unsold with 213,000, while 2,407 seats for athletics and thousands of day passes for the Olympic Park also went spare. In addition, 55,000 Paralympics tickets went unsold.
However 2.5m Olympic and 2.1m Paralympic tickets were sold for £20 or less. The figures, published in a letter to the London Assembly will be used to question London 2012 chief Lord Deighton and chairman Lord Coe today.
"[London 2012] set out its commitments and aims for the Olympic and Paralympic ticketing programme which were to raise over £500m towards the cost of staging the Games, fill our venues, and offer affordable and accessible tickets," wrote Deighton. "I am delighted to confirm that we have met all these commitments and aims."