Her father, William Joseph Smithson, was an actor and theatrical manager from Gloucestershire, England, and her mother was an actress whose full name is unknown.

[1] In October 1801, Harriet was left in the care of Reverend James Barrett, a priest of the Church of Ireland, parish of Drumcliffe.

[2] On 27 May 1814, Smithson made her first stage appearance at the Theatre Royal (Dublin), as Albina Mandevill in Frederick Reynolds's The Will.

She certainly is a most interesting and promising young actress, and there is no doubt she would prove a great acquisition to Crow-street, in the line of performance which her taste, as well as her talents, incline her to pursue.

[2] Four years later, 20 January 1818, Smithson made her first London appearance at Drury Lane as Letitia Hardy in The Belle's Stratagem.

On 20 February 1821, she took the lead female role in Thérèse by John Howard Payne, when the cast actress fell ill.[2] Overall, the London public remembered her as The Times put it, "a face and features well adapted to her profession; but [an actress] not likely to make a great impression on a London audience, or to figure among stars of the first magnitude.

Though she received negative reviews for this role, she was highly praised for her beauty and ability in the subsequent performance of She Stoops to Conquer.

[2] She left a long lasting impression on the French through her interpretation of Ophelia's madness, utilizing pantomime and natural presentation.

Miss Smithson acted the scene in which, robbed of her sanity, she takes her own veil to be her father's body with utmost grace and truth.

[2] Until this point, women's lines in theatre were heavily cut and censored to reduce the role for the company's "restricted talent.

This scene is extremely beautiful, even though it is written with a studied refinement...Miss Smithson could not have been more graceful upon the balcony; her posture were full of truth, grace, and love...In her strong moments, she is no longer a woman, but a Fury or something approaching that...[7]On 18 September, Shakespeare's Othello became the third Shakespeare tragedy to be performed by The English theatre.

[2] The English Theatre replaced the productions of tragedies with comedies, such as The Belle's Stratagem, The School for Scandal, Mrs. Centlivre's The Wonder, and Mrs. Cowley's The Weathercock.

[10] After Covent Garden closed for the summer in 1832, Smithson toured England to minor theatres performing almost exclusively in tragedies.

[2] The many French Romantic pieces of art, plays, music, and written works she had inspired depicted her as Ophelia, Juliet, and Harriet.

After Berlioz saw Smithson as Ophelia in 1827, he became infatuated with her, or rather with "a dramatic image [of a woman] lent force by supreme art of Shakespeare and intensity by a highly charged occasion and performance.

[11] Berlioz discovered Smithson at the Odéon Theatre performing the roles of Juliet Capulet and Ophelia and immediately fell in love with her.