When the Second World War began, she joined the French Red Cross being assigned to the Anglo-American Ambulance Corps. The Allied collapse in May 1940 prevented her evacuation from France and she remained there until the summer of 1941 when she escaped to England via Spain and Portugal.
In September of 1941, she joined the Women's Auxillary Air Force, working at the Department of the Chief of Air Staff as Assistant Section Officer for Intelligence duties, before being posted to Moreton-in-the-Marsh, where she was promoted to Section Officer.
She first came to the attention of the Special Operations Executive when Harry Sporborg, a senior SOE staff member, saw her file and requested that she be appointed his secretary. Having already joined the WAAF, she began military training instead. some months later she happened to meet Squadron Leader William Simpson, who worked part-time for SOE and with whom she discussed her desire to return to France and take part in resistance work.
In early March 1943, she received an invitation to a preliminary interview with an officer of SOE F Section, and on 18th. March began her training.
On June 16th. 1943 she was flown to a location north of Angers, in the Loire Valley, in occupied France with fellow agents Noor Inayat Khan and Cicely Lefort, where they were met by Henri Dericourt, the air movements officer for F Section. From there she made her way to Saint-Amour where she was assigned to the Acrobat network led by John Starr.
Her duties included acting as a courier, delivering messages to other agents and members of the underground in Marseille, Lyon and Paris. She also helped Harry Rée plan the destruction of the Peugeot factory in Sochaux, where tank turrets and aircraft engine parts were made.
A month after Rowden's arrival, network leader John Starr was arrested. Rowden and wireless operator John Young took refuge with a french family at the village of Clairvaux-les-Lacs, near Lons-le-Saunier.
In mid-November 1943, they were told by wireless from Baker Street to expect the arrival of a new agent. On 18th. Noember the new arrival appeared, but turned out to be a false agent planted by the Germans. Rowden and Young were arrested that evening and taken to Lons-le-Saunier.
Next day, Rowden was taken to 84, Avenue Foch, the Paris headquarters of the Sicherheitsdienst, where she was interrogated for two weeks before being sent to Fresnes prison.
On the 13th. May 1944, Diana Rowden, along with arrested SOE agents Sonya Olschanezky, Andrée Borrel, Yolande Beekman, Vera Leigh, Eliane Plewman, Odette Sansom-Hallowes and Madeleine Damerment were moved to concentration camps in Germany.
On 6th. July 1944, Rowden, Leigh, Borrel and Olschanezky were shipped to the Natzweiler-Struthof concentration camp in the Vosges Mountains of Alsace, where they are thought to have been injected with phenol and disposed of in the crematorium. They were meant to disappear without a trace, but their arrival at the concentration camp was witnessed by captured SOE agent Brian Stonehouse and Albert Guérisse, a member of the Belgian resistance.
Posthumously she was created an MBE and was awarded the Croix de Guerre. her name is registered with the Scottish National War Memorial in Edingburgh Castle, at Runnymede Memorial in Surrey and on the 'Roll of Honour' on the Valençay SOE Memorial in the town of Valençay, in the Indre département of France.
The concentration camp where she died is now a French government historical site: a plaque to Diana Rowden and the three women who died with her is part of the Deportation Memorial on the site. In 1985, SOE agent and painter Brian Stonehouse, who saw Diana Rowden and the three other female SOE agents just before their deaths, painted a watercolour of the four women which now hangs in the Special Forces Club in London.