"I lived my childhood outside, riding motorbikes, docking sheep and feeding out on tractors."
She completed a BSc in zoology and psychology at the University of Canterbury. Seeing potential career opportunities in the recently passed Resource Management Act, she went on to do the university's newly created postgraduate diploma in environmental science.
After graduating, she found the first of her ideal jobs, working for a D'Urville Island-based company advising its clients on mussel farm resource applications. After a year, she set up her own company Resource Management Consulting, with the support of a key client, the Yealands family.
Well known for their winery, the Yealands were pioneers of mussel farming.
Mussel farming was a lucrative business during the early 1990s, but environmental pressure and iwi concerns saw the government place a moratorium on new permits in 1996.
Ms Brennan took advantage of the downtime to focus on rowing, which she had begun in her 20s with immediate success. She was eventually shoulder-tapped to relocate to Cambridge where she focused on the sport fulltime for almost five years while studying for a law degree at Waikato University.
But disaster struck a couple of months out from travelling with the New Zealand Women's Eight in 1999 for a European tour, which she hoped would result in selection for the 2000 Sydney Olympics. She broke a rib and underwent six weeks of intensive physio, only to break the rib again on her first team training row.
Olympic hopes shattered, she shifted focus to her law degree, but the Yealands family came calling again. The moratorium was lifted in 1999 and they wanted her to work on permitting again.
She went back into fulltime consulting in Blenheim, but by 2001 she wanted a change and moved to an Auckland position as a forestry consenting consultant.
However, the tragic early death of her brother resulted in her moving back to spend time with her parents and sister-in-law, now based at a farm in Hunterville.
"I really re-assessed my life and where I was going," she said, adding that the grieving process also saw her finally coming to terms with the end of her Olympic dream.
Deciding to pursue her love of adventure, she moved to National Park and in 2002 completed the six-month Outdoor Pursuits Centre instructor course. She also met her future husband, a well-known outdoor pursuits instructor. They moved to Waitomo and set up a company that took teenagers on week-long wilderness adventure trips.
The marriage ended and after a year or so in Cambridge, she and her young son relocated in 2008 to Tauranga.
Her role as programme coordinator for Smart Growth was a test of her project and people management skills, she said.
"But I absolutely loved it."
Chamber of Commerce operations, events and training manager Anne Pankhurst said Ms Brennan was the kind of young leader the Bay needed.
"Justine has a unique quality of being able to listen, acknowledge your position and then disagree with you in the most charming way. Which of course means you feel valued and listened too, but challenged.
"When Justine worked with SmartGrowth this trait is what was valued most, followed closely by her very sharp intellect. Her new role with Bay Venues will really suit her."