Welby, the Archbishop of Canterbury said the controversial plan of Prime Minister Rishi Sunak's Conservative government would "outsource our legal and moral responsibilities for refugees and asylum seekers".
He made the comments during a debate in parliament's unelected upper chamber the House of Lords, which is scrutinizing the government's Safety of Rwanda (Asylum and Immigration) Bill.
"With this bill, the government is continuing to seek good objectives in the wrong way, leading the nation down a damaging path," said Welby, the highest-ranking cleric in the Church of England, the mother church of global Anglicanism.
The legislation aims to combat irregular immigration by deporting asylum seekers to Rwanda.
Sunak has put the plan at the center of his pledge to "stop the boats" of migrants crossing the Channel from northern France in flimsy and ill-suited vessels.
FILE — Britain's Prime Minister Rishi Sunak hosts a press conference inside the Downing Street Briefing Room, in central London on January 18, 2024, following the passing of the government's Rwanda Bill in the House of Commons.
The bill is Sunak’s answer to a UK Supreme Court ruling passed late last year.
The ruling said deporting asylum seekers to the East African nation is illegal under international law. If passed, the legislation would compel judges to treat Rwanda as a safe third country. It would also give UK ministers powers to disregard sections of international and British human rights legislation.
Welby, one of 26 senior Church of England bishops and archbishops who sit as the Lords Spiritual in the House of Lords, said the bill was damaging for asylum seekers in need of protection and safe legal routes.
He added that it was also damaging for Britain's "reputation" in relation to international law.
"Worst of all, it is damaging for our nation's unity in a time when the greatest issues of war, peace, defense and security need us to be united," the archbishop said.