- In a warning shot ahead of the debate, Suella Braverman said the bill, passed by MPs last month, represents "the will of the British people".
- Writing in the Times with new Justice Secretary Alex Chalk, she added that it had been "improved" during its passage through the House of Commons.
The Archbishop of Canterbury has attacked the government's migration plans, saying they risked "great damage" to the UK's reputation.
Justin Welby said the Illegal Migration Bill would not stop small boat crossings, and it failed in "our moral responsibly" towards refugees.
He was speaking as the bill begins what is expected to be a rocky passage through the House of Lords.
However, the home secretary has urged peers to get behind the legislation.
In a warning shot ahead of the debate, Suella Braverman said the bill, passed by MPs last month, represents "the will of the British people".
Writing in the Times with new Justice Secretary Alex Chalk, she added that it had been "improved" during its passage through the House of Commons.
The bill, unveiled in March, is a key part of Prime Minister Rishi Sunak's plan to "stop" small boats crossing the English Channel - which he has made a priority ahead of the next general election.
It will place a legal duty on the home secretary to detain and remove those arriving in the UK illegally, to Rwanda or another "safe" third country.
This has prompted outrage from opposition parties and charities, which argue the bill is unworkable and could breach international law.
The archbishop, one of nearly 90 peers who have put their names down to speak in the debate, told the Lords the bill "fails utterly" to take long-term view of the migration challenges around the world.
'Short-term fix'
Although he conceded existing international law was in need of updating, he said the bill represented a "dramatic departure" from existing conventions and would undermine international co-operation on the issue.
Describing the bill as a "short-term fix," he said it "risks great damage to the UK's interests and reputation, at home and abroad".
The government made a series of concessions to different sections of the Conservative Party to ease its passage through the Commons last month.
However, senior peers have told the BBC they expect significant opposition in the Lords - where the government does not have a majority.
Although peers will not vote on amendments during the debate later, it will be their first chance to have their say on the bill and represents a chance for them to scope out support for possible changes to the bill at a later stage.
Lib Dem peer Lord Paddick has put forward a rare "motion to decline" that would block the bill from continuing in the Lords, forcing the government to reintroduce it from scratch in the Commons.
However, this is unlikely to happen because Labour has confirmed it will not be supporting the motion.
Labour peer Lord Coaker said that although his party was against the bill, and the Lib Dem motion "sounds attractive", it was not the best way to oppose it.
He added that this was because the government was likely to reintroduce the bill anyway, without peers getting the opportunity to make any amendments.
He said Labour would do "all we can" to change the bill at a later stage, vowing that the would not be "cowed" into accepting the verdict of the Commons.
The bill showed the government was playing "fast and loose with our place in the world, and our respect for international law," he added.
Modern slavery concerns
Several peers have already spoken out against changes giving ministers more leeway to ignore attempts by European judges to halt deportations of migrants from the UK.
The government has also faced strong criticism from senior Tories, including former Prime Minister Theresa May and former Tory leader Sir Iain Duncan Smith, over the potential impact of the bill on victims of modern slavery.
The bill would take away temporary protections against removal from the UK that are currently offered to suspected victims of modern slavery or human trafficking while their case is considered.
Critics say this could deter victims from going to the police.
There has also been concern, including among Conservative MPs, over new powers in the bill to detain children on the suspicion that they are liable for removal.
Ministers have agreed to work with Tory MPs on a time limit for how long unaccompanied children can be detained.
To get the bill through the Commons, ministers also promised to set out new safe and legal routes for asylum seekers, after pressure from backbenchers.