It came as the retail firm unveiled a new brand, Made With Care, designed by people who have grown up in the care system.
The boss of the John Lewis Partnership has called on the Government to make being in care a protected characteristic, meaning it would be illegal to discriminate against them.
Dame Sharon White also said she has put pressure on current policymakers and Labour to introduce longer-term support for care leavers.
It came as the retail firm unveiled a new brand, Made With Care, designed by people who have grown up in the care system, which it will sell in shops before Christmas.
Last year, the department store business focussed on a child in care in its popular Christmas advert and has since raised more than £1 million for its Building Happier Futures programme aimed at supporting care leavers.
At an event at its Odney Club venue in Cookham, Berkshire, Dame Sharon told partners from the business and charity partners that it is seeking to help a “community that has been failed by the state”.
She told the PA news agency: “We must be the employer of choice for young people who have been brought up in care.
“There is this systemic failure and there is a particular cliff edge with care.
“You reach the age of 18 and suddenly you’re on your own with no access to social work, school, no access to home, and you’re then having to sort of navigate the system with even less support.”
The company chairwoman, who earlier this month announced her plan to step down in early 2025, said she has sought cross-party support to make being from care a protected characteristic.
It came as John Lewis confirmed it will sell a tote bag as the first item in its Made With Care programme on December 12.
The bag was designed by Michael Archibald, an 18-year-old aspiring artist from Glasgow who has experienced care.
“Creative industries are such a competitive field and being given the chance to work with such big companies makes me feel like I’m able to go places,” Mr Archibald said.
“I want more care-experienced people to feel this way.
“I’m so excited by the potential of Made With Care to give more people like me a platform to be creative and raise more awareness at the same time.”
Johnny Mercer MP, who was appointed a cross-government lead for care leavers, told PA he wants the UK to be the “best country” for someone to be a care leaver.
“All people want to see better outcomes for care leavers so I going to try and break a few eggs and make a good fist of securing those outcomes,” he said.
“I can completely understand why people are frustrated with the situation, but to be fair to government, they do put more money into this stuff over time and that is indisputable.
“At the same time, people are not feeling that progress at the speed that they should be feeling it.”