During the Second World War, his father was an aircraftman in the Royal Air Force, and was a wireless operator in a mobile signals unit in Burma and India.

He was educated at Kilmarnock Academy and as a youth earned a private pilot's licence through the Air Training Corps flying scholarship scheme.

[2][3] During his military career, he studied social sciences with the Open University, graduating with a Bachelor of Arts (BA) degree in 1998.

[4] He undertook a Master of Arts (MA) degree in defence studies at King's College, London, graduating in 1999.

[8] He was promoted to squadron leader on 1 July 1991[9] and wing commander on 1 July 1996,[10] and was awarded the Distinguished Flying Cross for his actions commanding II (AC) Squadron in the Gulf during Operation Southern Watch on 29 October 1999.

[11] Promoted to group captain on 1 July 2000,[12] Hillier became station commander at RAF Lossiemouth.