It is thought to be the deadliest ever attack on Pakistan's Christians.
A faction of the Pakistani Taliban said it ordered the attack to retaliate against US drone strikes.
Political and religious leaders condemned the attack, but angry crowds took to the streets denouncing the state's failure to protect minorities.
On Sunday, demonstrators blocked roads in Peshawar, Islamabad, Lahore and Karachi and rallies are also expected in major cities on Monday.
Condemnation of the attack has been pouring in. The government has announced three days of mourning.
Christian groups have said special prayers will be held for the victims. Pope Francis has condemned the atrocity, saying those who carried out the attack made a wrong choice, of hatred and war.
Sunday Mass attacked
Speaking in London on his way to New York to attend the UN's General Assembly, Prime Minister Nawaz Sharif said the attack does not bode well for any intended talks with militants.
And the Pakistani politician, Imran Khan, whose party governs the Khyber Pakhtunkhwa province, of which Peshawar is the capital, called it an attack on humanity.
He has been criticised for being soft on Taliban militants and favouring talks instead of military action.
At around midday at the historic All Saints church in Kohati Gate, a bustling area of Peshawar, two bombers blew themselves up as hundreds of worshippers who had attended Sunday Mass were leaving.
Witnesses said they heard two blasts, the second more powerful than the first. Suicide vests were later found outside the church, officials said.
Reports say the walls of the church was dimpled from the force of the ball bearings that had been packed into the explosives, in an effort to cause as much damage as possible.
More than 120 people were wounded in the assault.
The militant group, Jandullah, linked to the Pakistani Taliban, said they carried out the double bombing in retaliation for US drone strikes in Pakistan's tribal north-west.
It is the latest in a series of attacks on Pakistani Christians, who represent about 1.6% of the country's overwhelmingly Muslim population.
One provincial lawmaker, Fredrich Azeem Ghauri, said there were about 200,000 Christians in the province, of whom 70,000 lived in Peshawar, Agence France-Presse news agency reported.
The BBC's Shahzeb Jillani in Pakistan says the attack has outraged many people, but there is also a sense of helplessness about the government's apparent inability to prevent such atrocities.
There were angry scenes outside the church, with friends and relatives denouncing the government, but demonstrations spread rapidly and in Karachi police had to fire tear gas.
Militants in Pakistan have long made religious minorities one of their targets and recent years have seen spiralling sectarian violence between Shias and Sunnis, with Sunni militants often targeting the Shia community.
There have been outbreaks of communal violence in areas where Muslims and Christians co-exist. In march, Muslims in Lahore torched dozens of Christian homes responding to an allegation of blasphemy.
But this latest attack is being described as the first assault of its kind on Christians in recent memory.