The key issue now is whether the ruling coalition, which had pushed for Mr Musharraf's exit since winning the February election, can stay united and deliver on its promises, he says.
It will have to agree on a new president, then persuade allies like the US and UK, and its neighbours like India and Afghanistan, that it will be committed to defeating militancy and terrorism, our correspondent adds.
International reaction to Mr Musharraf's resignation was mixed, with the US hailing him as strong ally against terrorism but Afghanistan welcoming his departure as a boost to democracy.
Looking calm and dressed soberly in a dark suit and tie, Mr Musharraf said he had decided to resign after consulting his allies and advisers.
The eventual new president must be elected by both houses of Pakistan's parliament and the four provincial assemblies.
Reacting to news of the resignation, US Secretary of State Condoleezza Rice praised him as a "friend to the United States and one of the world's most committed partners in the war against terrorism and extremism".
She said the US would work with Pakistan's new leaders, pressing on them the need to stem "the growth of extremism".
The UK government wished Mr Musharraf well but stressed that relations did not depend on one individual.
India said it had no comment to make on the resignation since it was an internal matter for Pakistan.
Neighbouring Afghanistan, whose own president, Hamid Karzai, had a very fraught relationship with Mr Musharraf, hoped his departure would boost democracy in both countries.
Mr Musharraf's resignation followed more than a year of turbulence.
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