Nick Clegg has announced suicidal patients will be given the same priority as heart attack victims as part of an effort to increase resources for those with mental health problems.
Waiting times for mentally ill patients in England will be introduced for the first time with some conditions being put on the same footing as cancer.
Most people with depression who need talking therapies will begin treatment within six weeks.
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Young people hit by psychosis for the first time should be seen within two weeks - the same target as cancer patients - when the changes come into force next April.
Clegg will tell activists at the Liberal Democrat party conference in Glasgow the £120 million plan is the first step in reforming "Cinderella" mental health services.
Liberal Democrats would extend reforms to other areas, such as bipolar and eating disorders, in a future government using half of the extra £1 billion that would be raised from tax measures hitting the wealthiest that they would plough into the NHS.
The Deputy Prime Minister will use his keynote speech today to put the shake-up at the heart of the Lib Dem general election campaign - even though he concedes the move will not be popular with all of his party.
Clegg will tell activists: "For the first time ever, we will introduce national waiting times for patients with mental health conditions.
"Labour introduced waiting times in physical health - we will do the same for the many people struggling with conditions that you often can't see, that we often don't talk about, but which are just as serious.
"So if you are waiting for talking therapies to help with your depression, you will be seen within six weeks - 18 weeks at an absolute maximum - just as if you are waiting for an operation on your hip.
"If you are a young person experiencing psychosis for the first time, you will be seen within two weeks, something we are going to roll out across the country - just as if you suspect you have cancer.
"If you are having a breakdown, if you are thinking of harming yourself, for any emergency which takes you to A&E, you'll get the help you need - just as if you had gone to hospital with chest pains or following an accident.
"These are big, big changes. And in government again the Liberal Democrats will commit to completing this overhaul of our mental health services, ending the discrimination against mental health for good.
"And while I know not everyone in the party is going to agree, I can tell you now, I want this smack bang on the front page of our next manifesto."
Aides said Clegg has not suffered from any mental illness but has campaigned on improving treatment for patients his "whole political career" after seeing first hand as an MP the struggle some people have.
Mental health problems are estimated to cost the economy around £100 billion a year and around 70 million working days are also lost annually.
Clegg will say: "I have campaigned to end the Cinderella treatment of mental health services ever since, because it threatens the opportunities available to hundreds and thousands of our fellow citizens.
"Anxiety, panic attacks, depression, anorexia, bulimia, self-harm, bipolar disorder - these and many other mental health conditions are one of the last remaining taboos in our society, and yet they will affect one in four people.
"Much progress has been made - people now speak out in the way they never did before, we have put mental health on the same legal footing in the NHS as physical health, we're massively expanding talking therapies and transforming the help children can get as they move into adulthood - but there's still a long, long way to go.
"I want this to be a country where a young dad chatting at the school gates will feel as comfortable discussing anxiety, stress, depression as the mum who's explaining how she sprained her ankle."
Mark Winstanley, chief executive officer at Rethink Mental Illness, said: "This is a watershed moment for everyone affected by mental illness and has the potential to improve the lives of millions.
"No one should have to wait months or even years for potentially life-changing treatment, just because they have a mental health problem rather than a physical one. Together with our supporters, we have been campaigning for maximum waiting times for many years."
Sarah Brennan, chief executive of YoungMinds, said: "We welcome this announcement which is really good news in terms of confronting the glaring gaps in the parity of esteem between physical and mental health services especially around waiting times.
"We also warmly welcome the financial resources being put into inpatient care and the five-year plan for improving mental health services."
Centre for Mental Health chief executive Sean Duggan said: "The provision of additional funding to invest in crisis care and early intervention should help to overcome the current postcode lottery in access to these essential health services."
NHS England estimated the cost to the UK of mental illness to be as much as £100 billion each year through lost working days, benefits and treating preventable illness as a result of mental illness and expected the plan to claw back some savings.
These include £44m per year saved due to reduced hospital admissions for psychosis patients, around £5m saved through improved A&E psychiatric liaison services and a reduction in the estimated 70 million working days lost.
Simon Stevens, NHS England's chief executive, said: "This is an important moment when we will bring parity of esteem for mental health services a step closer. Putting access and waiting standards in place across all mental health services, and delivering better integration of physical and mental health care by 2020, will bring us much closer towards that aim."
Dr Geraldine Strathdee, NHS England's national clinical director for mental health, said: "This programme will start the journey to transform mental health care in England. Today people who present in crisis often wait too long for an assessment and to access treatment.
"This new approach will help improve crisis care and help reduce the distress that untreated mental illness brings. With 75% of long term mental health problems diagnosed before 18, investing in early effective treatments will pay immediate and long-term dividends."
Health Minister Norman Lamb said it was "outrageous" that mental health patients did not have the same waiting time targets as people with other conditions.
He told BBC Radio 4's Today programme: "This is a simple fact of discrimination. If you have cancer you get access to a specialist within two weeks. If you have a first episode of psychosis it's completely haphazard.
"That is outrageous. There's both a moral and an economic case to do this."
He said the Lib Dems will press for extra funding for the NHS in Chancellor George Osborne's Autumn Statement.
"We have been very clear that the NHS needs more funding. We are the only party that's come out and said that in 2015/16, in other words next year, the NHS needs a funding boost.
"It will be our top priority for the Autumn Statement to argue the case for extra funding."
Lamb, who has been tipped as a potential successor to Clegg, insisted that "nobody" had said the Deputy Prime Minister was not up to the job.
But he said he would consider a run for the leadership once Clegg decides to stand down.
He said: "I am a very, very strong supporter of Nick. I think, in time, people will recognise the extraordinarily important role he has played, and in delivering political stability at a time of economic distress, that is a priceless commodity.
"I absolutely don't want to replace Nick Clegg.
"When he stands down, I haven't ruled out standing for the leadership myself. That's the extent of it. We'll cross that bridge when we come to it, in the meantime I think he has performed brilliantly in government, securing this country's economic future."