[1] Campbell was born Beatrice Rose Stella Tanner in Kensington, London, to John Tanner (1829–1895), son and heir of a wealthy British Army contractor to the British East India Company, and Maria Luigia Giovanna ("Louisa Joanna") née Romanini (1836–1908), daughter of Italian Count Angelo Romanini.

She became successful after starring in Sir Arthur Wing Pinero's play, The Second Mrs Tanqueray (1893) at St. James's Theatre where she also appeared in The Masqueraders (1894).

Once established as a major star, Campbell assisted in the early careers of some noted actors, such as Gerald Du Maurier and George Arliss.

Other performances included roles in The Joy of Living (1902), Pelléas et Mélisande (1904; as Melisande to the Pelleas of her friend Sarah Bernhardt), Hedda Gabler (1907), Electra, The Thunderbolt (both 1908), and Bella Donna (1911).

In 1914, she played Eliza Doolittle in the original West End production of Pygmalion, which George Bernard Shaw had expressly written for her.

[11] Her last major stage role was in the Broadway production of Ivor Novello's play A Party, where she portrayed the cigar-smoking, Pekingese-wielding actress Mrs. MacDonald – a clear takeoff on her own well-known persona – and made off with the best reviews.

Her tendency, however, to reject roles that could have vitally helped her career in later years caused Alexander Woollcott to declare "... she was like a sinking ship firing on the rescuers".

[12] In the late 1890s, Campbell first became aware of George Bernard Shaw – the famous and feared dramatic critic for The Saturday Review – who lavishly praised her better performances and thoroughly criticised her lesser efforts.

[13] Not until 1912, when they began negotiations for the London production of Pygmalion, did Shaw develop an infatuation for Campbell that resulted in a passionate, yet unconsummated, love affair of mutual fascination and a legendary exchange of letters.

They remained friends in spite of the break-up and her subsequent marriage to George Cornwallis-West, but Shaw never again allowed her to originate any of the roles he had written with her in mind (e.g. Hesione Hushabye in Heartbreak House, the Serpent in Back to Methuselah, etc.).

[27] Their daughter Stella (1886–1975)[28] also joined her mother onstage, and toured with her in the United States, but "made up her mind to marry a man [Beatrice] scarcely knew, who had lived in Africa for many years".

A number of her letters and her annotated script for Chester Bailey Fernald's The Moonlight Blossom are in the theatre manuscripts collection of the Harry Ransom Center, University of Texas at Austin.

In 1957, the play Dear Liar by Jerome Kilty, an adaptation of the epistolary exchanges between Campbell and Shaw, was first staged in Chicago.