Neagle proved to be a box-office sensation in British films for over 25 years. She was noted for providing glamour and sophistication to war-torn London audiences with her lightweight musicals, comedies and historical dramas. She won several awards as Britain's favourite actress and biggest female box-office draw. Almost all of her films were produced and directed by Herbert Wilcox, whom she married in 1943.

In her historical dramas, Neagle was renowned for her portrayals of real-life British heroines, including Nell Gwynn (Nell Gwynn, 1934), Queen Victoria (Victoria the Great, 1937, and Sixty Glorious Years, 1938) and Edith Cavell (Nurse Edith Cavell, 1939).

Neagle was born in Forest Gate, Essex (now Greater London), daughter to Herbert Robertson, a merchant navy captain, and his wife, the former Florence Neagle. Robertson attended St. Albans High School for Girls.[citation needed] She made her stage debut as a dancer in 1917, and later appeared in the chorus of C.B. Cochran's revues and also André Charlot's revue Bubbly. While with Cochran she understudied Jessie Matthews.

In 1931 she starred in the West End musical Stand Up and Sing (1931), with actor Jack Buchanan, who encouraged her to take a featured role. For this play she began using the professional name of Anna Neagle (the surname being her mother's maiden name). The play was a huge success with a total run of 604 performances. Stand Up and Sing provided her big break when film producer and director Herbert Wilcox, who had caught the show purposely to consider Buchanan for an upcoming film, but also took note of her cinematic potential.

Naturally enough when I was a young dancer, I was terribly anxious to get ahead, and to get ahead quickly. I was impatient with all those older people who talked of the long grind to the top, who turned me down for jobs I knew I could do.

Forming a professional alliance with Wilcox, Neagle played her first starring film role in the musical Goodnight Vienna (1932), again with Jack Buchanan. With this film Neagle became an overnight favourite. Although the film cost a mere £23,000 to a produce, it was a huge hit at the box office, profits from its Australian release alone being £150,000.

After her starring role in The Flag Lieutenant that same year, directed by and co-starring Henry Edwards, she worked exclusively under Wilcox's direction for all but one of her subsequent films, becoming one of Britain's biggest stars.

She continued in the musical genre, co-starring with Fernand Graavey (later known as Fernand Gravet) in Bitter Sweet (1933). This first version of Noel Coward's tale of ill-fated lovers was later obscured by the more famous Jeanette MacDonald-Nelson Eddy remade from 1940.

Neagle had her first major success with in Nell Gwyn (1934), which Wilcox had also shot in 1926 as a silent starring Dorothy Gish. Neagle's performance as the woman who became the mistress of Charles II (Sir Cedric Hardwicke) prompted some censorship in the United States. The Hays Office had Wilcox add a (historically false) scene featuring the two leads getting married and also a "framing" story resulting in an entirely different ending. Noted writer Graham Greene said of Nell Gwynn: "I have seen few things more attractive than Miss Neagle in breeches".

Two years after Nell Gwynn, she followed up with another true-life figure, portraying Irish actress Peg Woffington in Peg of Old Drury (1936). That same year she appeared in Limelight, a backstage musical in which she played a chorus girl. Her co-star was Arthur Tracy, who had gained fame in the United States as a radio performer known as 'The Street Singer'. The film also featured Jack Buchanan in an unbilled cameo. performing "Goodnight Vienna".