The flag has been created by outdoor agency Curb and spans 540 square metres, measuring 30 metres in height. It marks the first time an image has been painted on Heathrow's airfield.
It is positioned next to the northern runway so passengers can see the image as their flights land.
Red carpets will be laid out across arrivals halls in the airport and Diamond Jubilee and Union Jack flags will be handed out. There will also be live music performances.
An array of congratulatory messages will be collected from consumers to be sent to the Queen.
The activity comes amid a Heathrow marketing campaign reassuring consumers that the BAA-owned airport will deliver a smooth Olympic run during the Games period, but also amid long immigration queues at the airport that have spoiled first impressions for foreign visitors.
Heathrow is expecting more than 2.9 million visitors over the next fortnight, with 780,000 passengers predicted to arrive between 30 May and 6 June.
John Holland-Kaye, commercial director, Heathrow, said: "The Queen's Diamond Jubilee celebrations mark the start of an important and historic summer for Heathrow.
"As the UK's hub Airport, we are delighted to welcome thousands of visitors to Heathrow to celebrate this momentous national occasion."
Follow Loulla-Mae Eleftheriou-Smith at @loullamae_es