On graduating in 1943, Park turned down jobs in the Treasury and the Foreign Office to make a direct contribution to the war effort.

On her return in 1946 she was sent to Vienna to establish an office for the Field Intelligence Agency Technical (FIAT), a unit of the Allied Commission responsible for tracking down former Axis scientists.

In 1948, she was attached to the Foreign Office, while actually working for the Secret Intelligence Service (SIS, aka MI6), becoming Third Secretary of the United Kingdom's delegation to NATO in 1952.

British parliamentarian David Lea wrote that shortly before she died, she claimed to have been involved in organising the abduction and murder of Patrice Lumumba during the Congo Crisis.

Park (allegedly) confided to Lea that the reasoning behind the assassination was MI6 fears that Lumumba would hand over the high-value Katangese uranium deposits of Shinkolobwe as well as the diamonds and other important minerals largely located in the secessionist eastern state of Katanga to the Russians.

[9] On 27 February 1990, she was created a life peer Baroness Park of Monmouth, of Broadway in the County of Hereford and Worcester,[10][11] and served as SIS's semi-official spokesperson in the House of Lords.

[13][14] A Service of Thanksgiving for the Life and Work of Baroness Park was held on Tuesday 26 October 2010 and the eulogy was given by fellow ex-spy Sir Mark Allen, CMG.