A study by the charity of 274 of its care leaver services cases found that 125 young people had mental health needs but 81 (65 per cent) were not receiving specialist support from a mental health service.
The study also found that one in four (69) care leavers had experienced a mental health crisis since leaving care.
Barnardo's chief executive Javed Khan is calling on the government to ensure that some of the £1.4bn in additional funding pledged to improve children's mental health is used to support care leavers.
"Our research shows a shocking picture of care leavers in need with no access to suitable mental health support," Khan said.
"Young people who have been in care often experience poor mental health ranging from anxiety to serious problems following abuse or neglect.
"The government must ensure these vulnerable young people receive the support they so desperately need when it honours its pledge to improve children's mental health."
The charity is specifically calling for a mental health worker to be embedded within leaving care teams.
It also wants to see improved mental health training among those working in care leaver services. The study found that many care leaver professionals do not have a good understanding of how to support young people's mental health needs.
The Local Government Association (LGA) said government must ensure extra money is made available to improve access to support for all young people with mental health problems.
"Children come into care in the most difficult circumstances, and giving them the best opportunities to overcome these and get a good start in life is a major focus for councils. This is particularly true as they move from care into adulthood," said LGA children and young people board chairman Richard Watts.
"Whilst this research rightly highlights that care leavers are more likely to experience poorer mental health than the general population, we must do more to ensure that all children and young people are able to access emotional health and wellbeing support whenever they need it," he added.
In July the government published its mental health workforce plan that included a pledge to improve access by recruiting an additional 2,000 child and adolescent mental health services staff within the next three years. But the British Association of Social Workers is concerned that social workers are being frozen out of the plans.
The Department of Health has been contacted for comment.