Mental health teams will be placed in police stations and courts to help cut reoffending.
The pilot scheme was launched by the Barnet, Haringey and Enfield Mental Health Trust on Friday.
It is hoped the project will help tackle the high rate of mental health needs amongst people in the criminal justice system.
Lord Victor Adebowale, chairman of the Independent Commission on Mental Health and Policing, said: “The high rates of mental health issues amongst prisoners suggest that the prison service has become a catch-all social and mental healthcare service, as well as a breeding ground for poor mental health.
"I welcome the pilot, as research has shown that investing in diversion now will make huge financial savings in the long term, improving mental health and reducing reoffending.”
Doctors and police officers hope the scheme will reduce the burden on the criminal justice system by saving police and court time.
It will also allow vulnerable adults with suspected mental health issues, learning disabilities and substance misuse problems, to be assessed and referred for treatment.
Maria Kane, CEO of Barnet, Enfield and Haringey Mental Health NHS Trust, said: “We are delighted that north east London has been chosen to pilot this very worthy programme.
“Our trust has a long tradition of working alongside the criminal justice system and I look forward to continuing to work with our partners to reduce health inequalities and repeat offending in the local population.”