"I did everything in my power not to be here anymore so when I woke up and the doctor told me I was lucky I knew I had been given a second chance.
"From then on, every single day I open my eyes I want to make a positive impact on somebody's life - helping people helps me."
Speaking to an audience of about 150 young people, Williams said it was his career in boxing that taught him how to fight life.
"I've come up against some pretty fierce guys on the field and even fiercer guys in the ring but nothing has compared to what I come up against inside my own head.
"If you give up in the boxing ring you get hurt. If you give up on mental illness, you die. Some days it will be a battle but now I know it will never beat me."
He said it was important for indigenous youth to remember that while friends came and went, their culture and ancestors didn't.
"The voices in my head still tell me I'm not good enough but the one thing that has always had my back is my ancestors and my culture. It's important to find your culture and live it."
The conference was organised by Te Runanga o Ngati Pikiao Trust and is believed to be the first of its kind in the world, attracting indigenous cultures from around the globe.
Project leader Michael Naera said he was amazed at the response on the first day.
"We were aiming for 200 people and on our first day we had 480 registered."
Where to get help: Youth services: 06 3555 906
- Youthline: 0800 376 633
- Kidsline: 0800 543 754 (4pm to 6pm weekdays)
- Whatsup: 0800 942 8787 (noon to midnight)
- Depression helpline: 0800 111 757 (24-hour service)
- Rainbow Youth: 09 376 4155
- If it is an emergency and you feel like you or someone else is at risk, call 111