Major General Sir Denzil Macarthur-Onslow, CBE, DSO, ED (5 March 1904 – 30 November 1984) was an Australian Army officer, businessman and grazier.

In 1935, he was appointed captain Ex Reserve of Officers in the 2nd Military District of the Australian Field Artillery; on 31 June 1936 he was appointed a captain in the Royal Australian Artillery.

He was promoted major in October 1939 and served with the 6th Australian Division Reconnaissance Regiment.

He was discharged in August 1953 but re-enlisted in August 1954, commanding the 2nd Division; he transferred to the Reserve on 1 December 1957 and was appointed to the Military Board on 1 December 1958 as a major general.

[2] Macarthur-Onslow was also politically active; he was by far the most successful candidate for the Liberal Democratic Party at the 1943 federal election, coming close to winning the seat of Eden-Monaro.