[9] Clifford was born in London on 7 April 1982, the daughter of an executive assistant mother and a father who works for the local council.

[12][13] In the first ten years of her professional acting career, Clifford became a prolific Off West End actress.

[15] Her first notable performance was playing Ismene in the Nottingham Playhouse production of Burial at Thebes at the Barbican which premiered in September 2007.

[16][17] In Summer 2008, she acted in a play called The Pendulum, written by her co-star Alexander Fiske-Harrison, at the Jermyn Street Theatre in the West End, which ran for the month of June,[18] and in the following month she took part in the annual Latitude Festival in the play Public Displays of Affection.

[19] Clifford was in three theatre productions the next summer; in June she had a small role in a chamber opera titled Parthenogenesis at the Royal Opera House's Linbury Studio,[20] she co-starred in the Arcola Theatre play The Road to Mecca,[21][22] and she toured with the production Is Everyone Okay?

[25][26][27] For the rest of autumn 2010, she had a supporting role in the play Pains of Youth at the prestigious Royal National Theatre.

[28][29] Finishing out the year, Clifford held the titular role in an original production of Beauty and the Beast, also at the Royal National Theatre.

[35] In 2018, she had a recurring role in the ITV miniseries Vanity Fair and was in a production of Circle Mirror Transformation in Manchester.

She starred opposite Matthew Macfadyen in the April 2020 miniseries Quiz, based on the 2001 Charles Ingram Who Wants to Be A Millionaire?

[42] In July 2024, Clifford starred as journalist Chloe Slack in Time of the Week, a BBC Radio 4 comedy series.