Gregory holds a MSc in Environmental-Health issues (Paris-Saclay University), a Post-Graduate Certificate in Water, sanitation and hygiene (WEDC, Loughborough University) and in Environmental management (University College Dublin).

He started to work as humanitarian officer in 2001 in Albania with Solidarites International. He then worked with various organizations such as Action Against Hunger, the French Red Cross, Solidarités International again and Unicef in multiple countries across Africa, Central America and Asia. Gregory coordinated the national response to the cholera outbreak in Haiti from 2014 to 2018 as UNICEF Emergency Chief, before joining UNICEF HQ as WASH Emergency Response Team member until February 2021. He is now with UNDP as Malaria Program Manager in Haiti.