A surprised Weatherall was awarded the Tony Jackson Scholarship to compete in the event in front of family, friends and workmates last week.
Weatherall splits his time between working as a ambulance paramedic and crewing in the Otago Rescue Helicopter.
A large part of his time is spent helping people struggling with mental health issues.
Weatherall is looking to use his participation in the Ironman to highlight the work of mental health awareness organisation The Key To Life Trust.
''This gives me an awesome and really positive opportunity to spread the word about mental health,'' he said.
''We all have medical and physical health and we all have mental health, but this does not mean mental illness.
''Approximately 30% of my work as a paramedic is attending people having a really challenging time of things in regard to their mental health.''
The New Zealand Ironman is held over the traditional distance of a 3.8km swim, 180km bike ride and a 42.2km run.
''It's certainly going to be a big day at the office.''
Previous sporting events should mean those gruelling distances are within Weatherall's reach.
He formerly represented Otago and New Zealand in surf life-saving.
Weatherall completed the two-day event at the Coast to Coast late last year.
He was originally planning to compete in next year's Challenge Wanaka, but his scholarship offer means he is starting to prepare for the Ironman in Taupo in March immediately.
Weatherall thinks he has everything he needs to prepare for the event in and around Dunedin.
''We have got a pretty cool harbour here, we have got pretty cool roads you can ride and some pretty cool tracks you can run on.''
''The open water of the harbour should replicate the Taupo lake on a rough day.''
