Discharging around 25,000 patients to free up beds was an example of the government’s "slow, inconsistent and at times negligent" approach to social care, the cross-party Public Accounts Committee (PAC) said.
It added that it was "concerned" that the Department of Health and Social Care (DHSC) had continued with the policy "even once it was clear there was an emerging problem".
ITV News obtained the discharges data in June, and found 25,060 people were discharged from hospital into care homes without being routinely tested for Covid-19 in England.
It was only on April 16 that blanket testing of all discharges began.
Ministers have rejected the criticisms of the PAC report, with Culture Secretary Oliver Dowden defending the government by saying there were 40% less discharges from hospitals into care homes than the previous year.
"I don't accept the characterisation of the Public Accounts Committee," he told ITV News.
"We were in the middle of a pandemic and we were being accused of checking people out of hospitals into care homes carrying Covid.
"Actually, there were fewer people discharged from hospital into care homes during that period than in the previous year," he said.
He appeared to concede errors had been made, but said they were addressed "immediately".
"Of course there were challenges in care homes and we accepted those challenges, we've accepted there were lessons to learn. And indeed we took action immediately."
He added: "For example with our care home action plan, we've ensured that everyone, whether they are residents or whether they are staff whether they have symptoms or not."
Hospitals in England were asked on March 17 to discharge patients, but patients did not require a coronavirus test prior to discharge until April 15.
And it was the end of April when the government said all care home residents and staff, regardless of symptoms, would be able to access tests.
This is despite Public Health England (PHE) telling the committee it was aware of asymptomatic transmission as early as the end of March.
Committee Chair Meg Hillier told ITV News that by "readying the NHS for Covid-19, care homes were thrown to the winds".
"They didn't have the right support, the right information and there was such a lack of understanding about the care sector - which is something we've criticised before as a committee - it's extraordinary, really, that it wasn't thought through in advance," she said.
She added how the "greatest failing was to put people into care homes from hospitals".
"The line went out, get people out of hospital if they're medically safe to be discharged, but they didn't do Covid tests, they didn't even assess whether that would be a risk in care homes."
She said "people were dying in their homes that they lived in because of this negligent approach".
In evidence on June 22, PHE’s Professor Paul Johnstone said:
"What was becoming clear in the back-end of March and certainly from the beginning of April was that there was an asymptomatic phase, which means that people can transfer the virus without ever having symptoms, or a significant pre-symptomatic phase, which is where the virus could be shared."
The DHSC told the committee in the same session it believes the clearest correlations between social care outbreaks related to staff rather than the discharge of hospital patients.
However, it added: "That is not the same as saying that we would do the same again."
The PAC said nobody would expect the government to get everything right in its initial response, but that it "urgently needs to reflect, acknowledge its mistakes, and learn from them".
ITV News spoke to managing director of Saint Cecilia’s nursing home in Scarborough at the end of May. At that point the care home had fifteen beds block booked at the beginning of the pandemic to take in hospital patients.
But managing director Mike Padgham told ITV News he had little choice but to continue accepting Covid-19 patients - given the financial pressures he faces and the need to help the NHS.
Care home bosses have been critical of the government throughout the pandemic.
In early July, Downing Street declined to apologise after Boris Johnson suggested “too many” care homes had not properly follow procedures during the outbreak.
Care home manager Debbie Adams branded the PM a "joke" over the comments, adding that she was "absolutely livid" and accused the government of not knowing what the correct procedure to follow was.
Care home manager Debbie Adams told ITV News the PM 'needs to apologise' for saying 'too many care homes didn't follow procedure':
The PAC report flagged testing as another issue. It said that testing should have been made available to hospital patients and social care staff "much more quickly".
And it identified a lack of transparency around the availability of personal protective equipment (PPE), with a tendency for the government to "overpromise and under deliver".
Committee chair, MP Meg Hillier, said: "The failure to provide adequate PPE or testing to the millions of staff and volunteers who risked their lives to help us through the first peak of the crisis is a sad, low moment in our national response.
"Our care homes were effectively thrown to the wolves, and the virus has ravaged some of them."
She added: "The deaths of people in care homes devastated many, many families.
"They and we don’t have time for promises and slogans, or exercises in blame.
"We weren’t prepared for the first wave," she continued.
"Putting all else aside, government must use the narrow window we have now to plan for a second wave.
"Lives depend upon getting our response right."
The report, Readying the NHS and social care for the Covid-19 peak, is the PAC’s first examination of the health and social care response to the crisis.
It also said it was concerned about a "scarcity of information on contracts and costs" during the period, when NHS England and Improvement said hundreds of thousands of patient treatments had been secured through independent hospitals.
The committee said it was concerned that NHS England and Improvement had not provided a rough estimate of costs.And it said allowing the Nightingale hospitals to remain empty while the NHS requires additional capacity for routine services "will not be a good use of public money'.
It is calling for the DHSC and NHS to write to the committee by September 1 detailing how private and Nightingale hospitals will be "made best use of" in the coming months.
A DHSC spokesperson said: "Throughout this unprecedented global pandemic we have been working closely with the sector and public health experts to put in place guidance and support for adult social care.
"Alongside an extra £1.3 billion to support the hospital discharge process, we have provided 172 million items of PPE to the social care sector since the start of the pandemic and are testing all residents and staff, including repeat testing for staff and residents in care homes for over-65 or those with dementia.
"We know there is a need for a long-term solution for social care and we will bring forward a plan that puts social care on a sustainable footing to ensure the reforms will last long into the future."