The board has decided that it will stop the global chief executive search as it reviews the co-op's "current portfolio and direction".
"It's important that we give ourselves the time to take stock of where we are as a co-operative, breathe some fresh air into the business, then determine any changes that are needed.
"Appointing a new chief executive is the most critical decision a board will make. We will take all the time we need to find the right person.
"In the meantime, we need a new leader that can hit the ground running," Monaghan said.
"Miles has great mana. He has a deep understanding of our business and has demonstrated his ability to manage large, complex business units in most of our global markets," Monaghan said.
Hurrell said he was excited by the challenge.
"I've been part of the Co-operative for 18 years and understand that its true potential really comes down to its people.
"Theo leaves behind a talented leadership team that includes some of the best minds in global dairy," he said.
"I've been privileged to be part of that group for the last four years and I'm totally confident that, by working as a team, we can deliver on the expectations New Zealand has of us," he said.
"We are already a number of weeks into our new financial year, so I'm keen to get straight into it and ensure the business lives up to the commitments it has made to our farmers and unitholders for the year ahead."
Monaghan said the board and Spierings had agreed it was the right time for him to step down as chief executive.
Spierings would work alongside Hurrell to ensure a smooth transition of leadership through to September 1, the company said.
Before being appointed CEO, Hurrell led Fonterra's global Co-operative farming strategy which includes farmer services, engagement, milk sourcing and the chain of 70 Farm Source rural retail stores throughout New Zealand.
In his previous role as General Manager Middle East, Africa and CIS he led a period of sustained growth during a time of political unrest across the region.
He reset the African sales strategy and was a director of Fonterra's joint venture with Africa's largest dairy company, Clover Industries Limited.
In 2006-2008, Hurrell oversaw the streamlining of the Co-operative's European operations before moving to the United States to establish new offshore partnerships.
In 2014, Hurrell was appointed the Co-operative Affairs Group Director and in 2016 he took up the role as Chief Operating Officer of Farm Source.
Fonterra last week shocked investors and farmers with an earnings downgrade.
In the face of high debt and tight margins, Fonterra pared back its farmgate milk price for the season just ended and ditched plans for a second-half dividend in a bid to shore up its balance sheet.
Fonterra said it would cut its 2017-18 milk price forecast by 5c to $6.70 per kg, and won't pay farmers and investors a dividend for the second half of that financial year.
Fonterra affirmed its guidance for normalised earnings per share, at 25-30 cents, but indicated that they were likely to be at or slightly below that range.
The co-op anticipated that no dividends would be paid for the year, beyond the 10c per share interim payment made in April.
Farmgate milk prices are dictated by Fonterra's Milk Price Manual, which was how the original $6.75 forecast was arrived at. But in just the second time in Fonterra's nearly two-decade history, the company has crimped the milk price - its biggest input cost - in order to benefit earnings.
MILES HURRELL
• Born: 1974, Christchurch, New Zealand
• Nationality: New Zealand
• Education:
- INSEAD (International Executive Development)
- London Business School (Finance)
- Kellogg's North Western University (Global Sales)
- International Institute for Management Development (IMD) Switzerland
