Survivors and families of those who lost their lives in the terror attacks will lay flowers by 52 steel pillars which represent those killed.
A wreath will be laid in the name of Prime Minister David Cameron as a one-minute silence is held at midday.
Four suicide bombers detonated explosives on board three Tube trains and a bus during rush hour in 2005.
Security Minister Dame Pauline Neville-Jones will speak at the Chatham House conference, which aims to reflect on the response that followed the attacks and assess what threats remain.
From the archives: 5 years on from 7/7 see how a fledgling blog covered the events as they happened http://bit.ly/dnNoQy
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Coincidence can bring mixed fortune and sometimes it can be cruel. Many passengers on the number 30 were only using it because the Tube was closed due to Hussain’s three fellow bombers detonating their devices. Something they did not know as they boarded it.
I still can’t explain… the series of coincidences that puts a bus on diversion where it shouldn’t be, to blow up outside a building full of doctors Dr Peter Holden
But chance can also bring unexpected blessings. The unfolding drama on that day meant the bus was forced to take a detour which delivered it into the hands of one of the few people in the country trained to handle a major emergency on that scale – Dr Holden.
The bus was torn apart in front of the headquarters of the British Medical Association (BMA), where he was attending committee meetings. A GP by trade, he is also trained as one of the UK’s few major incident commanders.
“I thought ‘I really am in it now’,” he says. “Then I thought ‘you’ve been trained for this – come on’.”
By yet another coincidence, a medical conference was also being held at the BMA. It meant dozens of doctors were on hand to offer lifesaving expertise.