One of the most popular film and music stars of the 1930s and 1940s, Marlene Dietrich was known for her fashionable style and diverse portrayals of women. She was a firm advocate for the American war effort, contributing much of her time, energy and musical talents to aid the troops.

In 1920s Berlin, Dietrich performed on the stage and in silent films. Her performance as Lola-Lola in Josef von Sternberg's The Blue Angel (1930) brought her international acclaim and a contract with Paramount Pictures. She starred in many Hollywood films, including six iconic roles directed by Sternberg: Morocco (1930) (her only Academy Award nomination), Dishonored (1931), Shanghai Express and Blonde Venus (both 1932), The Scarlet Empress (1934) and The Devil Is a Woman (1935), Desire (1936) and Destry Rides Again (1939). She successfully traded on her glamorous persona and exotic looks, and became one of the era's highest-paid actresses. Throughout World War II she was a high-profile entertainer in the United States. Although she delivered notable performances in several post-war films, including Billy Wilder's A Foreign Affair (1948), Alfred Hitchcock's Stage Fright (1950), Billy Wilder's Witness for the Prosecution (1957), Orson Welles's Touch of Evil (1958) and Stanley Kramer's Judgment at Nuremberg (1961), she spent most of the 1950s to the 1970s touring the world as a marquee live-show performer.

Dietrich was known for her humanitarian efforts during World War II, housing German and French exiles, providing financial support and even advocating their American citizenship. For her work on improving morale on the front lines during the war, she received several honors from the United States, France, Belgium and Israel. In 1999, the American Film Institute named Dietrich the ninth greatest female screen legend of classic Hollywood cinema.

In 1930, on the strength of The Blue Angel's international success, and with encouragement and promotion from Josef von Sternberg, who was established in Hollywood, Dietrich moved to the United States under contract to Paramount Pictures, the U.S. film distributor of The Blue Angel. The studio sought to market Dietrich as a German answer to Metro-Goldwyn-Mayer's Swedish-born star, Greta Garbo. Sternberg welcomed her with gifts, including a green Rolls-Royce Phantom II. The car later appeared in their first U.S. film Morocco.

Dietrich starred in six films directed by von Sternberg at Paramount between 1930 and 1935. Von Sternberg worked effectively with Dietrich to create the image of a glamorous and mysterious femme fatale. He encouraged her to lose weight and coached her intensively as an actress. She willingly followed his sometimes imperious direction in a way that a number of other performers resisted.

In Morocco (1930) with Gary Cooper, Dietrich was again cast as a cabaret singer. The film is best remembered for the sequence in which she performs a song dressed in a man's white tie and kisses another woman, both provocative for the era. The film earned Dietrich her only Academy Award nomination

Dietrich was known to have strong political convictions and the mind to speak them. In the late 1930s, Dietrich created a fund with Billy Wilder and several other exiles to help Jews and dissidents escape from Germany. In 1937, her entire salary for Knight Without Armor ($450,000) was put into escrow to help the refugees. In 1939, she became an American citizen and renounced her German citizenship.In December 1941, the U.S. entered World War II, and Dietrich became one of the first public figures to help sell war bonds. She toured the U.S. from January 1942 to September 1943 (appearing before 250,000 troops on the Pacific Coast leg of her tour alone) and was reported to have sold more war bonds than any other star.

During two extended tours for the USO in 1944 and 1945, she performed for Allied troops in Algeria, Italy, the UK, France and Heerlen in the Netherlands, then entered Germany with Generals James M. Gavin and George S. Patton. When asked why she had done this, in spite of the obvious danger of being within a few kilometers of German lines, she replied, "aus Anstand"—"out of decency". Wilder later remarked that she was at the front lines more than Dwight Eisenhower. Her revue, with Danny Thomas as her opening act for the first tour, included songs from her films, performances on her musical saw (a skill taught to her by Igo Sym that she had originally acquired for stage appearances in Berlin in the 1920s) and a "mindreading" act that her friend Orson Welles had taught her for his Mercury Wonder Show. Dietrich would inform the audience that she could read minds and ask them to concentrate on whatever came into their minds. Then she would walk over to a soldier and earnestly tell him, "Oh, think of something else. I can't possibly talk about that!" American church papers reportedly published stories complaining about this part of Dietrich's act.

In 1944, the Morale Operations Branch of the Office of Strategic Services (OSS) initiated the Musak project, musical propaganda broadcasts designed to demoralize enemy soldiers. Dietrich, the only performer who was made aware that her recordings would be for OSS use, recorded a number of songs in German for the project, including "Lili Marleen", a favorite of soldiers on both sides of the conflict. Major General William J. Donovan, head of the OSS, wrote to Dietrich, "I am personally deeply grateful for your generosity in making these recordings for us.

At the war's end in Europe, Dietrich reunited with her sister Elisabeth and her sister's husband and son. They had resided in the German village of Belsen throughout the war years, running a cinema frequented by Nazi officers and officials who oversaw the Bergen-Belsen concentration camp. Dietrich's mother remained in Berlin during the war; her husband moved to a ranch in the San Fernando Valley of California. Dietrich vouched for her sister and her sister's husband, sheltering them from possible prosecution as Nazi collaborators. However, Dietrich later omitted the existence of her sister and her sister's son from all accounts of her life, completely disowning them and claiming to be an only child.

Dietrich received the Medal of Freedom in November 1947, for her "extraordinary record entertaining troops overseas during the war". She said this was her proudest accomplishment. She was also awarded the Légion d'honneur by the French government for her wartime work.