The Australian prime minister, John Howard, his counterpart from New Zealand, Helen Clark and Prince Charles were among the dignitaries who attended the remembrance service.
It began as a full moon shone above the Dardanelles straits with the prince reading a sombre psalm. He and other dignitaries later laid wreathes at the Helles Point clifftop battle memorial.
With no Gallipoli veterans present at the ceremony, the crowd was swelled by thousands of backpackers from Australia and New Zealand. Many had slept out in the open overnight, and watched wrapped in flags or with their faces painted.
In Sydney, a record crowd of more than 20,000 people took part in an Anzac Day service and the Queen and the Duke of Edinburgh were to attend a similiar event at Westminster Abbey.
Yesterday there was a ceremony in Gallipoli to honour the fallen Turkish troops, which was attended by the Turkish prime minister, Recep Tayyip Erdogan, Ms Clark and Mr Howard.
The Gallipoli campaign, which began on April 25 1915, saw tens of thousands of troops lose their lives as they landed on the peninsula in one of the Britain's worst military disasters. At the height of the fighting, the waters around the peninsula were said be reddened with blood as far as 50 metres from the shore.
Winston Churchill, then first lord of the admiralty, and Lord Kitchener originally planned the attack, which was intended to capture Istanbul and clear a relief route to Russia by securing a passageway from the Mediterranean to the Black Sea.
Fierce resistance from the underrated Ottoman forces, inhospitable terrain and bungled planning led to a disaster that involved British, Irish, French, Indian, Australian and New Zealand forces. Around 9,000 Australian soldiers died.
Some 21,000 British and Irish troops were also killed, as were 9,000 French, though Gallipoli has come to be thought of as an Australian and New Zealand operation. Australian war correspondent and historian Charles Bean coined the term Anzac to mean Australian and New Zealand army corps.
Around 86,000 Turkish troops died defending the narrow peninsula in what the Turks call the Battle of Çanakkale. The campaign ended in stalemate and the Anzac forces were evacuated in December 1915.
Despite the terrible human toll, the campaign is seen as a landmark in the formation of a sense of national consciousness in both Australia and New Zealand. Mr Howard said during the remembrance service that the Anzacs had "changed forever" the way Australians saw themselves and their world.
"They bequeathed Australia a lasting sense of national identity, they sharpened our democratic temperament and our questioning eye towards authority.
"They came to do their bit in a mobilisation not of their making ... they forged a legend whose grip on us rises tighter with each passing year," he said.
Mrs Clark told the crowd: "It was here that our young nations began to come of age. It was here that we began to think of ourselves not just as servants of the British empire but as distinct national identities. Thus out of catastrophe each of our nations emerged with a new sense of certainty about our own destiny and our own place in the world."
The Helles Point memorial, on the southern tip of the peninsula, carries the names of 13,000 Commonwealth servicemen who were buried in unidentified graves and another 14,000 whose bodies were never found when the British were allowed back into Turkey after the end of the first world war.
Among the names on the monument is that of Corporal Orman Lankester, of Mistley, Essex. His niece, Hazel Smith, 55, from Kettering, Northamptonshire, was at the service today and laid her own personal wreath.
Ms Smith, who now lives in Istanbul, said: "I feel very proud but also I feel pretty sad. When I look at the sheer face of the cliffs and see how there was absolutely no chance for them, they were just like lambs to the slaughter."
