On 8 May 2000, Parker was commissioned into the Royal Army Chaplains' Department, British Army, as a Chaplain to the Forces 4th Class. [2] He was promoted to Chaplain to the Forces 3rd Class on 8 May 2006,[3] and to Chaplain to the Forces 2nd Class on 23 April 2012.[4] He served as chaplain to 4th Regiment Royal Artillery; 2nd Battalion, Princess of Wales's Royal Regiment; 1st Battalion, Royal Welch Fusiliers; 1st Battalion, Royal Regiment of Fusiliers; and 1st Battalion, Parachute Regiment.[5] He undertook operational tours to Northern Ireland, Iraq and Afghanistan.[6]
He attended the Advanced Command and Staff Course in 2013.[5] He was promoted to Chaplain to the Forces 1st Class on 30 June 2017 with seniority in that rank from the same date.[7] He then served as assistant chaplain general of the 3rd (United Kingdom) Division.[8]
Parker was appointed Deputy Chaplain-General to the Army in September 2020 and Chaplain-General to Her Majesty's Land Forces on 8 May 2022.[9][10] On 4 May 2023, he was made a Sarum Canon (i.e. honorary canon) of Salisbury Cathedral.[8][11]