Travers was born in Southern England, the daughter of a Royal Navy admiral, but grew up in the south of France, where she was a semi-professional tennis player.

At the outbreak of the Second World War, Travers joined the French Red Cross as a nurse, but later became an ambulance driver with the French Expeditionary Force in Finland. With the German invasion of Denmark and Norway, she retreated from Denmark to Finland. She then escaped by ship to Iceland and returned from there to England where she joined General De Gaulle's Free French forces. By 1941, she was the chauffeur for a medical officer of the 13th Demi-Brigade of the Foreign Legion, during the Syrian campaign in which Vichy French legionnaires fought Free French legionnaires. She was nicknamed "la Miss" by the legionnaires. She then travelled to North Africa via Dahomey and the Congo. During that journey, she had a brief affair with Georgian nobleman and Foreign Legion officer Dimitri Amilakhvari. She was then assigned as driver to Colonel Marie-Pierre Koenig and also became his lover.

In late May 1942, as the Afrika Korps prepared to attack Bir Hakeim, Koenig ordered Travers and other women out of the area. The Germans attacked on 26 May. Not long after, Travers joined a convoy into the rear area and Koenig agreed to her requests to return to Bir Hakeim, since he felt the German attack was a failure. However, during the following fortnight, the Luftwaffe flew 1,400 sorties against the defences of Bir Hakeim, whilst four German/Italian divisions attacked on the ground.

On 10 June, Travers drove Koenig's staff car during the retreat. The column ran into minefields and German machine gun fire. Koenig ordered Travers to drive at the front of the column. Travers stated:

He said, "We have to get in front. If we go the rest will follow." It is a delightful feeling, going as fast as you can in the dark. My main concern was that the engine would stall.

At 10:30 on 11 June, the column entered British lines. Travers' vehicle had been hit by eleven bullets, with a shock absorber destroyed and the brakes unserviceable. Her affair with Koenig ended after this battle, when he returned to his wife.

Travers went on to serve in Italy, France, and Germany, where she respectively drove an ambulance, lorry, and a self-propelled anti-tank gun. Later in the war, she was wounded when she drove over a mine.

After the war she was formally enrolled in the Légion Étrangère, as an Adjutant-Chef.

Travers served in Vietnam, during the First Indochina War. She married Adjutant-Chef Nicolas Schlegelmilch, who had fought at Bir Hakeim with the 13th Demi-Brigade. They had two sons. In retirement, they lived on the outskirts of Paris.

In 2000, aged 91, assisted by Taylor Holden she wrote her autobiography, Tomorrow to Be Brave: A Memoir of the Only Woman Ever to Serve in the French Foreign Legion, having waited for all the other principals in her life story to die before writing it.

Travers was decorated with the Légion d'honneur, Croix de Guerre and Médaille Militaire.

Susan Travers died at the age of 94. She was survived by a son, Thomas, and two granddaughters, Adela and Eleanor.