Julia Emilie Neilson (12 June 1868 – 27 May 1957) was an English actress best known for her numerous performances as Lady Blakeney in The Scarlet Pimpernel, for her roles in many tragedies and historical romances, and for her portrayal of Rosalind in a long-running production of As You Like It.

After establishing her reputation in a series of plays by W. S. Gilbert in 1888, Neilson joined the company of Herbert Beerbohm Tree, where she remained for five years, meeting her future husband, Fred Terry (brother to actresses Kate, Ellen, Marion and Florence Terry and great uncle of John Gielgud). With Terry, she played in London and on tour for nearly three decades. She was the mother of the actress Phyllis Neilson-Terry and actor Dennis Neilson-Terry.

Neilson was born in London, the only child of Alexander Ritchie Neilson, a jeweller, and his wife, Emilie Davis, a member of a family of five Jewish sisters, many of whose offspring became actresses. Neilson's parents divorced shortly after her birth, and her father soon died, leaving her mother to struggle to support her child. Her mother much later married a solicitor, William Morris, the widower of the actress Florence Terry, elder sister of the actor Fred Terry, who had, by that time, married Neilson.

Neilson was an indifferent student. At the age of twelve, she was sent to a boarding school in Wiesbaden, Germany, where she learned to speak French and German and began to study music, discovering that she excelled at this. She returned to England to enter the Royal Academy of Music in 1884, at the age of fifteen, to study piano. She soon discovered that she had a talent as a singer, winning the Llewellyn Thomas Gold Medal (1885), the Westmoreland Scholarship (1886) and the Sainton Dolby Prize (1886). While at the Academy, in 1887, she sang at the St James's Hall and also played roles in amateur theatre.

Neilson met the dramatist W. S. Gilbert, who cast her in her first professional stage appearance in March 1888. She played Cynisca in a charity matinée of his play, Pygmalion and Galatea, at the Lyceum Theatre, and later that year, in the same play, she was the lead character, Galatea, in a similar matinée at the Savoy Theatre. Gilbert suggested that the statuesque young woman concentrate her career on acting rather than singing, and he coached her on acting. Her next role was Lady Hilda in a revival of Gilbert's Broken Hearts. Gilbert wrote the lyrics to a short song for her to sing during Act I, and she proposed that a fellow student of hers at the Royal Academy, Edward German, should set it to music. She then played Selene in a revival of Gilbert's The Wicked World. In November 1888, she created the role of Ruth Redmayne in Rutland Barrington's production of Gilbert's Brantinghame Hall.

These roles led to an invitation for Neilson to join Herbert Beerbohm Tree's company, in which she toured in Captain Swift, The Red Lamp and The Merry Wives of Windsor. She remained with Tree's company for five years at the Haymarket Theatre as a tragedienne, beginning with the role of Julie de Noirville in A Man's Shadow, which opened in September 1889.^{[citation needed]}

In 1891, Neilson married another actor in the company, Fred Terry, the brother of Gilbert's former protégée, Marion Terry (and the actresses Kate, Ellen and Florence Terry). Neilson and her husband appeared together in Sydney Grundy's translation of the French play A Village Priest and numerous other productions together with Tree's company, including Beau Austin, Hamlet, Peril and Gilbert's Comedy and Tragedy (1890). She also played Drusilla Ives in The Dancing Girl (1891) by Henry Arthur Jones, and Terry and Neilson's daughter Phyllis was born in 1892. Neilson was soon back on stage as Lady Isobel in Jones's The Tempter (1893), and created the role of Hester Worsley in Oscar Wilde's A Woman of No Importance (1893).

A review of Neilson's performance in the play Ballad Monger in 1890 declared: