The number contacting the NSPCC's Childline hit record levels last year.
Girls were six times more likely to seek help for suicidal thoughts and feelings than boys and those at most risk were aged between 12 and 15.
Childline service manager for Northern Ireland Mairead Monds said: "We need to understand that there are children and young people living in Northern Ireland that are experiencing significant mental health problems, self-esteem issues, isolation and feelings of worthlessness.
"These are children who have very little support and who very often feel that life is simply not worth living.
"They see Childline as an essential line of support; we are there to listen to them and help them find a way to overcome their problems."
Childline carried out 349 suicide counselling sessions last year involving young people from Northern Ireland.
Children tended to feel more desperate in the winter months, with a third calling Childline counsellors at night, according to the service's annual report, It Turned Out Someone Did Care.
Many calls dealt with by counsellors were referred to emergency services.
Turbulent home life, abuse, school pressures, and mental health conditions were all major triggers for suicidal thoughts, with children as young as 10 describing how desperate they were, the report said.
One 17-year-old girl who contacted the counselling service's Belfast base said: "I've been having difficulties coping at college. I'm finding the lessons a struggle.
"In the past, I've had to take some time off because I've been suffering with mental health problems.
"Sometimes I feel so stressed and useless, I just have to walk out. I sometimes feel like I want to die."
There was a significant rise in the number of young people who spoke about their mental health, with a third of counselling sessions concentrating on the issue.
The chronic shortage of support is forcing many children to wait until they reach crisis point when they feel the only place they can turn to is Childline, the NSPCC said.
The organisation is calling for children and young people to feature as a priority group in the Department of Health's updated Protect Life Suicide Prevention Strategy.
Ms Monds added: "Our It's Time campaign is calling on government to fill a crucial gap in child protection and the calls we are increasingly receiving at Childline show just how urgently this is needed."