Her degree included a six month Erasmus exchange programme which she spent at Mary Immaculate College in Limerick. There she studied Irish history and geography. She graduated in 2000.

Her debut novel In and Out of the Goldfish Bowl was published the same year. An autobiographical account of a young girl growing up in the south Wales valleys against a backdrop of alcoholic and neglectful parents, sexual abuse, economic breakdown and a mounting drugs industry, the book was described by Time Out as “A pitiful tale, a triumphant achievement.” “… a child’s Christmas described in defiant, sulky rants in language that is acidic, inventive and scaldingly honest, it paints a despairing picture of drunken adults who spend their time thieving, quarrelling and annoying the police, before turning on their children because the neglected youngsters have been experimenting with drugs. Unemployment, rape and deprivation inflame this narrative” (Amazon).

In 2001, the book was included on the Orange Futures list, an initiative set up by The Orange Prize for Fiction to identify and promote the exciting writing of twenty one new young women authors at the beginning of the century. The book is studied in many Welsh Universities.

In 2002 Trezise was chosen by the Guardian Hay festival to be one of the first writers to take part in Scritture Giovani, a project conceived by Festivaletteratura (The Literary Festival of Mantova, Italy), Literaturfestival Berlin (The International Literature Festival of Berlin) and the Guardian Hay Festival with the intent of promoting young European writers by creating a network to spread the works written by up and coming young writers from each country. She travelled to all three festivals to read an unpublished short story written specifically for the project. It was during one of her onstage discussions in Italy that an audience member, a representative from Italian publishing company Einaudi, obtained the Italian rights to In and Out of the Goldfish Bowl. It was published in Italy in 2004 as La Mia Pelle Sporca. She was also voted by fashion magazine Harpers & Queen as the new face of literature in 2003. Director of the Guardian Hay Festival Peter Florence, writing for the magazine, said, ‘Rachel Trezise is the first writer of her generation to explore the territory of Welsh drug culture and poverty, and at the same time be laugh-out-loud funny. She’s a great comedian.’

Trezise began working as a freelance journalist, writing features on music and the arts for the Big Issue. Her essay about controversial Welsh artist Nealle Howells appeared in Sideways Glances ( Parthian, 2005). She also wrote short stories for Welsh anthologies Wales, Half Welsh (Bloomsbury, 2004) and Urban Welsh (Parthian, 2005). Her own short story collection Fresh Apples was published in 2005. Mario Basini, writing for the Western Mail, said, ‘The publication of this collection confirms the arrival of a major new literary talent, grown organically out of the unpromising valleys as flowers out of a bed of manure. At their best … they have the emotional power, the simplicity and directness of high quality art.’

Trezise’s music documentary and travelogue about a small Welsh band struggling to make the big time was published in 2007. Dial M for Merthyr follows Rachel on her travels with the band Midasuno as they tour the toilet circuit of Great Britain. She is currently working on her second novel, Sixteen Shades of Crazy, as well as various television and theatre pieces.

She enjoys writing, reading, music, art and baking, and dislikes violence, ignorance and animal cruelty. She still lives in the Rhondda with her partner and her cat.