McDonnell said Lunman was still available to help the new acting CEO and executive team.
Ferguson has also resigned. She had been Hatch's chief experience officer.
"We thank Natalie and Kristen for their respective contributions as our outgoing chief experience officer and CEO, and wish them the best for their next ventures," McDonnell said.
Lunman said she was still forming her plans for the future, but wanted to keep working in financial wellbeing and supporting women and families.
"Hatch is in a new phase now and is in great hands. With two of the founders staying on and a crack team, it is going from strength to strength inside FNZ as a global powerhouse," Lunman added.
Hatch was founded in 2018 to give consumers direct access to investing in US sharemarkets.
Kiwi Wealth sold Hatch to FNZ for an undisclosed sum last year.
FNZ said Hatch now served more than 130,000 users and more than NZ$2 billion had been transacted on the platform.
FNZ is a global financial technology firm that as of late last year had US$1.5 trillion in assets under administration.
When FNZ bought Hatch, it said Hatch would remain an autonomous business unit within the FNZ Group.
The deal would let Hatch retain and follow its entrepreneurial instincts while gaining access to FNZ's infrastructure and technology, FNZ said at the time.