Osama Bin Laden, who was responsible for some of the worst terrorist atrocities including the 9/11 attack, was killed in a US operation in Pakistan.
Mr Cameron congratulated President Obama on the operation and said now was a time to remember all those murdered by Osama Bin Laden.
The PM said:
The news that Osama Bin Laden is dead will bring great relief to people across the world. Osama Bin Laden was responsible for the worst terrorist atrocities the world has seen - for 9/11 and for so many attacks, which have cost thousands of lives, many of them British.
It is a great success that he has been found and will no longer be able to pursue his campaign of global terror. This is a time to remember all those murdered by Osama Bin Laden, and all those who lost loved ones. It is also a time too to thank all those who work round the clock to keep us safe from terrorism. Their work will continue.
I congratulate President Obama and those responsible for carrying out this operation.
Mr Cameron also spoke on television at his residence at Chequers. The Prime Minister said:
This news will be welcomed right across our country. Of course, it does not mark the end of the threat we face from extremist terrorism.
Indeed, we will have to be particularly vigilant in the weeks ahead. But it is, I believe, a massive step forward.
Osama bin Laden was responsible for the death of thousands of innocent men, women and children right across the world - people of every race and religion.
He was also responsible for ordering the death of many, many British citizens, both here and in other parts of the world.
I would like to congratulate the US forces who carried out this brave action. I would like to thank President Obama for ordering this action.
And I think it is a moment when we should thank all of those who work day and night, often with no recognition, to keep us safe from the threat of terror.
But above all today, we should think of the victims of the poisonous extremism that this man has been responsible for.
Of course, nothing will bring back those loved ones that families have lost to terror.
But at least they know the man who was responsible for these appalling acts is no more.