Allen is an internal promotion, and started at Fonterra as a graduate in 2008.
USX-listed company recently disclosed a $13.4m loss and held a $5.5m capital raise.
Amelia Linzey takes over from Greg Lowe in October.
Josh Barton will replace Marian Poirier, who is retiring after 30 years in the industry.
Wendy Jenkins has been with the company for just over a year.
Acting CEO Claire Falck has been appointed to the permanent role.
Both Pavanie Edirisuriya and Tom Barnes have been with DLA Piper for a number of years.
Very experienced Dr Thérèse Arseneau has been appointed to the role vacated by the retirement of Bryan Pearson.
Mark Pearce has more than 25 years of advisory experience.
Jess Bala will be managing director, GM Australia and New Zealand, effective from September 1.