The NHS number has seen a big rise in demand during the coronavirus pandemic.
The new mental health helpline is available round-the-clock for anyone after support or treatment from professionals.
The number, if you need it, is 01865 904997 for adults and 01865 904998 for children and young people.
The helpline is being launched by the Oxford Health NHS Foundation Trust, which runs local mental health services, with support from local charity Oxfordshire Mind.
It's for people whose situation it is not life threatening, and will operate 24 hours a day, seven days a week.
Rob Bale, clinical director at Oxford Health NHS Foundation Trust, said: "When people need non-emergency mental health care, support or advice they should call the 24/7 Oxfordshire and Buckinghamshire Mental Health Helpline.
"Our trained mental health advisors will be able to offer on-the-spot advice and make sure people get the care that is right for them."
During office hours, people who already use mental health services should contact those services directly using the numbers in their care plan.
The new helpline will operate during the coronavirus pandemic to provide people with specialist mental health care, as the NHS 111 number receives an increasing number of Covid-related calls.