The London Gang Exit programme will provide support to 300 young people aged 16 to 24 who are involved with a gang or at risk of becoming involved.
Young people referred to the programme will be allocated to a trained caseworker that will aim to provide intensive support for the young person and advocate on their behalf.
Support will focus on issues such as mental health problems, substance misuse support, employment and housing.
The initiative, which is being led by charity Safer London along with delivery partners Only Connect and youth charity Redthread, will also seek to help young women who are involved with gangs and may have been victims of sexual exploitation.
Referrals will come from teachers, care workers, police officers and other bodies such as prison and probation services.
Mayor of London Boris Johnson said: “This new London-wide service will give young people involved in or at risk from gangs the chance to turn their backs on violence and crime and transform their lives.”
Frances Mapstone, interim chief executive of Safer London said: “London Gang Exit is a unique new programme, in that it will ensure a consistent level of support to young people across London for the first time.
“This means that no matter which borough the young person lives in, they can receive help to exit gang life, stop offending and live safely.”