Zambellas was trained for the Naval Staff at Greenwich in 1990,[1] and after spending a short time as a corporate planner for the Royal Navy's manpower and training division within the Ministry of Defence, he took command of the mine-sweeperHMS Cattistock in 1991.[1] His next appointment was ashore, as an aviation operations officer in the Fleet Headquarters at Northwood, before being promoted to commander on 30 June 1994.[11] In 1995 he was given command of the frigateHMS Argyll and was deployed on counter-narcotics operations in the Caribbean.[1]
Zambellas was appointed Knight Commander of the Order of the Bath (KCB) in the 2012 Birthday Honours[19] and became First Sea Lord and Chief of the Naval Staff on 9 April 2013.[20][2] As of 2015, Zambellas was paid a salary of between £180,000 and £184,999 by the department, making him one of the 328 most highly paid people in the British public sector at that time.[21]
On 15 April 2014, in an op-ed article for the Daily Telegraph Zambellas laid out the case for a "No" vote at the 2014 Scottish independence referendum, stating that it would weaken British maritime defence.[22] Despite this, on 12 November 2014 he was publicly chastised by the UK Defence Secretary for suggesting to a journalist that the contract for Type 26 frigates may not be awarded to Scottish shipyards.[23][24]
On 4 July 2014, Zambellas was among those attending the launch ceremony of the 70,600-tonne Royal Navy aircraft carrier HMS Queen Elizabeth, the largest warship ever built in the United Kingdom, and formally named by Queen Elizabeth II.[25]