Two bombers blew themselves up as worshippers were coming out of the city's historic All Saints church after attending Sunday Mass, police say.
Relatives of the victims gathered at the scene to protest against the government's failure to protect them.
Militants linked to Pakistani Taliban have said they carried out the bombing.
The group, Jandullah, said it was in retaliation US drone strikes in Pakistan's tribal northwest.
Sunday's twin attacks targeted Peshawar's historic All Saints Church as hundreds of worshippers were attending Mass.
Witnesses said they heard two blasts, the second more powerful than the first.
Suicide vests were later found outside the church, officials say. More than 120 people were wounded in the bombings.
It is the latest in a series of attacks on Pakistani Christians, who represent about 1.6% of the country's largely Muslim population.
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.
Demonstrations were held in other cities too.
In Karachi, police fired bullets in air and tear gas to disperse hundreds of protesters.
A twin-suicide bombing outside a church in Peshawar in Pakistan has killed at least 75 people, in one of the worst attacks on Christians in the country.