The statement by Archbishop Socrates Villegas on behalf of the Catholic Bishops Conference comes ahead of a discussion in the House of Representatives regarding a bill to restore capital punishment for 21 crimes.
If the act passes, crimes including murder, rape, treason and car theft would be punishable by death.
Nine drug offences, including the sale, manufacture and possession of drugs, could also be punishable with the death penalty.
The death penalty was abolished in 2006 but President Rodrigo Duterte has said he would be "happy to slaughter" drug addicts.
Since he was elected in June 2016, more than 7,000 people have been killed in drug-related police operations, according to the Philippine National Police.
In a statement, Archbishop Villegas said: "It is this Gospel that we must uphold. We therefore unequivocally oppose proposals and moves to return the death penalty into the Philippine legal system.
"We took a considerable stride in the defense of life when we repealed the Heinous Crimes Act that provided for the death penalty in what were considered 'heinous crimes'. "
The Archbishop added that the trend against the death penalty can be observed throughout the world and the country would be taking a step backwards by reintroducing it.
"We urge the government to champion life for all!" Archbishop Villegas concluded.