Cardinal Malcolm Ranjith said the authorities had failed to identify those behind the suicide bombings that killed at least 258 people at three churches and three luxury hotels in Colombo.
"The executive and the legislature were locked in a power struggle. They did not care about the international conspiracy against the country," Ranjith said at the reconsecration one of the bombed churches.
He was referring to President Maithripala Sirisena's failed bid to oust his erstwhile ally, Prime Minister Ranil Wickremesinghe, and the ongoing power struggle between the two since October.
"The selfish power hungry leaders did not worry about ordinary people... The leaders did not heed intelligence warnings... the security council did not meet since October because of the power struggle," he said.
"The current leaders have failed. They have no backbone. They must leave the government and go home," Ranjith said.
In a hard-hitting sermon, Ranjith said he had no faith in the inquiries set up by the authorities to probe lapses leading to the April 21 bombings police have blamed on a local jihadi group.
"I have no faith in any of these committees and commissions of inquiry. These are election gimmicks. The leadership must allow someone else to run the country," the cardinal said.
There was no immediate comment from the government.
Ranjith also lambasted the United Nations, saying it was only interested in the welfare of the dozens of suspects arrested in connection with the bombings and not the plight of the survivors.
"The UN representatives ask about human rights and they visit those who are in detention, but not the victims," Ranjith said adding that Pope Francis gave him just over $90,000 last month to help the victims.
President Sirisena initially blamed Islamic extremists, but later began accusing international drug dealers of being behind the bombings, allegedly to destabilise his anti-narcotics drive.
The country's police chief and the then official in charge of the defence ministry are being prosecuted for not acting on prior information about the attacks.
Just over 100 people have also been arrested in connection with supporting the local National Thowheeth Jama'ath group to carry out the bombings. The Islamic State group also claimed responsibility.