Gallagher is from Andersonstown,[1] a suburb of West Belfast, and was born to father Daniel (d. 2017) from Tyrone and mother Pat.
[5] Gallagher made her television debut as Alicia Hodge in two 2009 episodes of the BBC One medical soap opera Doctors.
Her early stage work includes The Bloody Chamber and The Wicked Lady in England, and Be My Baby and Sleep Eat Party in Belfast.
She would return to the Lyric for Weddins, Weeins and Wakes, Demented, Pentecost, Stitched Up, Little Red Riding Hood, Love or Money, Smiley, and Bah, Humbug!.
[7] She also returned to A Midsummer Night's Dream, this time playing Hermia at Queen's Hall in Newtownards, went on tour with Is That Too Hot?, and appeared in The Real Housewives of Norn Iron at the Grand Opera House.
In 2021, it was announced Gallagher would star in her first lead television role as Shiv Sheridan in the BritBox and RTÉ comedy-drama The Dry, which premiered in 2022.