Following guest star appearances on shows such as The Bill, Birds of a Feather, and Peak Practice, she landed the part of staff nurse Rebecca Hopkins on ITV's Coronation Street; a role she played between 1999 and 2000.
[5] Halfpenny earned critical praise for her performance in The Bodies, a play adapted from an Émile Zola novel by Peter Flannery, which ran from June to July 2005 at Newcastle's Live Theatre.
[6] Describing her work as the "dangerously crazed" Thérèse, The Guardian commented, "Halfpenny, forced to remain impassive at the outset, is tough and moving in her portrayal of [the character's] descent into madness".
In his review for The Independent, critic Julian Hall felt that Halfpenny's performance "lends added zip to what is already a tightly written play ... [she] successfully evokes the tenacity that Farnes must have had to [endure Milligan]".
[19][20] In March 2012, Halfpenny headlined a revival of Mike Leigh's 1977 play Abigail's Party at the Menier Chocolate Factory, which later transferred to the West End's Wyndham's Theatre for four months.
[21] Her portrayal of the snobbish Beverly was warmly received, with The Guardian's Kate Kellaway calling her "fantastic", adding: [she] perfectly catches Bev's dark side – her selfishness, sexual frustration and dangerous stupidity".
[24] She then appeared as a timid middle-class holidaymaker in Alan Ayckbourn's Way Upstream at Chichester Festival Theatre (April to May 2015),[25] and played one of the principal characters—Jill Drummond, a disabled woman who falls for her humanoid caregiver—on the first season of the science fiction drama series Humans, which aired between June and August 2015.
[35] In Channel 5's The Drowning, a mystery thriller that aired over four consecutive nights in February 2021, Halfpenny starred as Jodie Walsh, a grief-stricken mother who comes to believe that her late son may still be alive.
Radio Times critic James Hibbs was effusive in his praise of the show's "strong" cast, calling them "real, fully rounded individuals" and adding, "Everyone brings their A-game in wholly different ways, [including] Halfpenny as the grieving mother of one of Sutcliffe's victims".
[37] Speaking of the research she undertook in preparation for playing Hill, Halfpenny said it was the lack of aftercare for the victims that shocked her most: "They were just left to deal with such tragic circumstances [and] in such a public arena, with seemingly no support ...
[38] Halfpenny's role in the 2024 adaptation of Shelagh Delaney's A Taste of Honey, which debuted at the Royal Exchange, Manchester on 15 March, was met with praise; writing for The Daily Telegraph, critic Mark Brown believed her portrayal of working-class single mother Helen to be "suitably monstrous, but with an intelligent, underlying and brittle fragility".
[40] Halfpenny has narrated commercials for Argos, Children in Need, Ford Fiesta, The Sunday Times, Aunt Bessie's, Cocoa Pops, the Royal Air Force, First Choice, and Caledonian Travel.