Dato Paduka Haji Mustappa bin Haji Sirat, DPMB, SMB, PJK, PIKB, BA (Hons) was born on 04th October 1957 in Belait, Brunei Darussalam.  He is married to Pengiran Datin Hajah Jamilah binti Pengiran Haji Mohd Yussof and has been blessed with one son, Mohd Reza Salmaan. 

Dato Paduka Haji Mustappa began his career as an Education Teacher at Berakas High School. He later joined the Ministry of Foreign Affairs in November 1982 and has held a range of appointments. Dato Paduka Haji Mustappa first overseas assignment was as 2nd Secretary at the Brunei Darussalam High Commission in London in September 1985. His consecutive overseas diplomatic appointments also took him to Paris and Geneva. 

In 2003, His Majesty The Sultan and Yang Di-Pertuan of Brunei Darussalam consented to appoint him as Brunei Darussalam High Commissioner to the Islamic Republic of Pakistan and served in that country on 18 March 2003 until 04 November 2004. Prior to that appointment, Dato Paduka Haji Mustappa was also the Director General of ASEAN-Brunei, and the Director of the Policy Planning  Department, Ministry of Foreign Affairs. On 25 October 2004, Haji Mustappa was appointed as Deputy Permanent Secretary II (Policy and Development) in the Ministry of Defence, and with effect from 03 Jun 2005, with the consent of His Majesty The Sultan and Yang Di-Pertuan of Brunei Darussalam, Dato Paduka Haji Mustappa was appointed as the Permanent Secretary of Defence. 

On 15 July 2006, Dato Paduka Haji Mustappa was conferred the Most Honourable Order of Paduka Mahkota Brunei, Second Class which carries the tittle “Dato Paduka”.