In 2008, Reese-Williams was cast to play the role of Gennie Walker in Emmerdale. The character was created by series producer Kathleen Beedles, although by the time Reese-Williams’s first episode aired on 1 April 2008, Anita Turner had taken over from Beedles. She was cast in the role and started filming in the week beginning 3 March 2008. It was announced that Reese-Williams was to leave the soap in 2013. Her character was killed off on 25 July 2013.

In 2012, she voiced the playable character of Boudica, the Welsh-speaking leader of the Celts, in Civilization V: Gods and Kings, an expansion pack of the video game Sid Meier’s Civilization V.

Following her stint in Emmerdale, Reese-Williams returned to theatre and in November 2013 played “Marta” in Children of Fate at the Bussey Building in Peckham.

In May/June 2014, she played ‘Linda’ in Alan Bennett’s Enjoy at the West Yorkshire Playhouse.

In 2016, she featured in series 3 of critically acclaimed Welsh crime drama Hinterland / Y Gwyll, playing DI Tom Matthias’s love interest, Manon.

In 2017, she starred in series 3 of the BAFTA award-winning 35 Diwrnod for S4C.

She played the role of Trudy in the BBC One/Netflix drama Requiem, which aired in early 2018, followed by the lead role of Detective Inspector Cadi John, in a bilingual crime drama that was shown on S4C in January 2018 as Craith, with English dialogue dubbed into Welsh, before being broadcast with bilingual dialogue on BBC Wales and BBC Four as Hidden in June 2018. A second series aired in 2019.

In January 2020, she appeared in Silent Witness as Tina Harcourt, a long time beaten wife who took revenge on the husbands & partners of other beaten women by killing some & framing others for those murders.