The Sudanese government and the biggest opposition grouping have signed a landmark reconciliation agreement.
NDA chairman Mohammed Osman al-Mirghani called for co-operation
The deal, signed in Cairo, brings the National Democratic Alliance (NDA) into a power-sharing administration set up with ex-southern rebels in January.
The NDA includes some of Sudan's oldest parties. They went into exile after the Islamist-backed 1989 coup that brought the current government to power.
The deal does not include the Darfur conflict - a big obstacle to peace.
January's peace agreement with the southern rebels ended more than 20 years of civil war.
'Backbone to unity'
There were cheers and applause as NDA chairman Mohammed Osman al-Mirghani signed the accord with Sudanese Vice-President Ali Osman Taha at a ceremony broadcast live by Egyptian television.
Egyptian President Hosni Mubarak attended the event, along with his Sudanese counterpart, Omar al-Bashir, the former southern rebel leader, John Garang, and the leadership of the opposition alliance.
"We are starting a new era where Sudan is free of struggle... Let us work hand in hand to offer the Sudanese the prosperity they have been lacking," said Mr Bashir.
"This latest agreement... will be the backbone of Sudanese unity," he said.
Mr Mirghani said the deal "heralds a new era in which all of us have to co-operate to achieve global peace, strengthen the march towards real democracy".
More than two million people have fled their homes in Darfur
The NDA alliance includes some of Sudan's oldest political parties, such as the Democratic Unionists, along with the Communists and various trade union and professional groups.
They will now take up seats in an interim government, broadening the base of support for the historic peace deal signed earlier this year to end the civil war in the south.
But according to the opposition alliance, key details have yet to be finalised, including of its share of seats in the administration and whether its fighters will be demobilised or integrated into the national army.
The Egyptian president said the Cairo accord "should serve as an inspiration for finding a settlement for Darfur, this crisis we all look forward to end".