[4] He received a Sixth Form scholarship from the Royal Air Force,[5] and was a member of the Army Cadets while at school.

[1][6] His rank was made substantive on 9 May 1992 and advanced to flying officer twelve months later,[7][8] before he was posted to the Harrier Force in 1995.

[1][14] Smyth was appointed Officer of the Order of the British Empire (OBE) in the 2011 New Year Honours,[15] was subsequently advanced to group captain, and appointed the United Kingdom's National Director of the Lockheed Martin F-35 Lightning II procurement programme in Washington, D.C.[1] He was aide-de-camp to The Queen from 13 December 2013 to 30 July 2015.

[16][17] As an air commodore, Smyth was appointed Honorary Colonel of the 2nd (Northern Ireland) Battalion, Army Cadet Force from 1 June 2016,[18] and attended the Higher Command and Staff Course at the Defence Academy of the United Kingdom in 2017.

[22] Reporting on Smyth's new post, Defense News wrote that "up to 25 civilians and military personnel involved in finance, policy and capabilities will support the new space directorate" in the Ministry of Defence's Main Building.

[25] In December 2023, it was announced that he would be the next Deputy Chief of the Defence Staff (Military Strategy and Operations); he succeeded Sir Roland Walker in the role in March 2024.