The Joseph Rowntree Foundation said 400,000 have already been served with an eviction notice or told they may be evicted.
The foundation said the temporary ban on bailiff-enforced evictions introduced in March 2020 – and extended several times since – has provided much-needed security to renters during the pandemic.
Its survey of more than 10,000 households suggested “clear warning signs” of a spike in evictions and homelessness as the ban lifts, the report said.
Around 400,000 are expecting to be evicted and a further 450,000 households are in arrears with rent, the foundation said.
Rachelle Earwaker, from the Joseph Rowntree Foundation, said: “For the 450,000 families locked in rent debt, the prospect of securing a mortgage is simply unimaginable and, worse still, many will now struggle to secure a new home in the private rented sector just as the eviction ban ends.
“High levels of arrears are restricting families’ ability to pay the bills and forcing many to rely on hidden borrowing.
“This is not only deeply unjust, it is also economically naive and risks hampering our economic recovery, which is reliant on household spending increasing as society continues to reopen.
“The Government’s decision to provide a generous tax break to wealthier homeowners through the stamp duty holiday while failing to protect renters points to a worrying two-tier recovery in which those who were prospering prior to the pandemic will continue to do so while those who have been hit hard will sink even further behind.
“The cost of boosting support to tackle rent arrears is a fraction of the cost of the stamp duty holiday.”
Alicia Kennedy, director of Generation Rent, an organisation representing private renters, described the government's decision to end the ban as “reckless”,
“If the government doesn't intervene, thousands of homeless families could be turning to their council for help,” she told the BBC.
“We can't build back better without financial support for the renters who have been hit hardest.”
The Ministry of Housing, Communities and Local Government said 45 per cent of private landlords own just one property and are highly vulnerable to rent arrears.
Housing Minister Christopher Pincher told the BBC: “As Covid restrictions are eased in line with the roadmap out of lockdown, we will ensure tenants continue to be supported with longer notice periods, while also balancing the need for landlords to access justice.”