The suicide bombers set off their devices as worshippers were leaving All Saints church at the end of Sunday Mass.
Jandullah, a militant group linked to the Taliban, has claimed responsibility for the attack, one of the worst against the country's persecuted Christian minority.
The bombing was carried out in retaliation for US drone strikes in Pakistan, Jandullah said.
Security has been heightened at other churches in Pakistan as a result of the attack, which has injured at least a hundred people.
Christians account for less than three per cent of the population in predominantly Muslim Pakistan,
Christian and human rights groups report frequent attacks on parts of the Christian community by Islamist extremists.
Sunday's attacks have sparked protests by Pakistani Christians angry over government inaction and a lack of protection from security forces.
Three days of mourning have been declared in Pakistan in response to the attacks.