Many are forced to rely on family and friends for the basic means to live, and some have been in this situation for more than a decade, said the charity the National Autistic Society (NAS).
The report - called Don't Write Me Off - found that a majority of the UK's more than 300,000 working age adults with autism want to work but are being held back by a lack of understanding of autism among advisers and a dearth of specialist employment services.
It discovered that almost 80% of people with autism on Incapacity Benefit want to work, while more than a third said their Disability Employment Adviser's knowledge of autism was "very bad" or "bad".
Half of people with autism have spent time with neither a job nor benefits, with more than three quarters of those forced to rely on family and friends as a result.
More than 82% needed some kind of help to apply for benefits, but few were made aware of their right to an advocate. In the worst cases parents were actively blocked from helping.
NAS chief executive Mark Lever said: "People with autism say their experiences of the employment and benefits system are marred by anxiety, confusion, delays and discrimination.
"It is absolutely vital they are able to access the right help and services if seeking employment and are supported financially when they cannot work.
"It is scandalous, therefore, that thousands of people with this serious, lifelong and disabling condition are being consigned to poverty by a complex and counter-productive benefits system."
The report also exposed common difficulties experienced by people with autism applying for the new Employment and Support Allowance (ESA), which replaced Incapacity Benefit.
A spokeswoman said it was clear the system was not working for them with many experiencing problems such as getting a sick note, filling in complex forms, poor medical assessments, being misdirected to the wrong benefits and not even being asked about their disability.
A spokeswoman for the Department for Work and Pensions said: "We understand that people with autism have complex needs so we have arrangements in place to help, such as bringing along someone to represent them in adviser interviews if needed.
"We are determined to provide the best support possible to help them get into work, which is why our wide range of personalised support looks at what people can do, rather than what they can't.
"We are working with the National Autistic Society and other organisations to ensure the right help is available for people with autism.
"The Government will be publishing its Autism Strategy in due course, which will set out our support for people with autism."