Séainín trained at the Irish Film Actors Studio.
Soon afterwards, she became the face of BBC 1 Friday Night Advertising.

Director Tom Poole then asked her to Guest star as Gabriella Fernando in the BBC NI premier sitcom Give My Head Peace and later in the new BBC NI drama I Fought the Law.

Meanwhile, Director Pam Brighton snapped her up to play Veronique in the Romantic Comedy Reprise by John P. Rooney for BBC Radio 4.

In London, Séainín was cast as the female lead in the Guinness film I Lose My Inhibitions. Later Séainín played the role of Sarah in a short film It's Not What You Say for Cambridge Film & TV Productions.

Séainín was then asked to play the lead role of Mary in a recorded workshop of the feature film The Rose of Tralee, before returning home to Ireland to provide the voice for Julie in the film Pretty Face for Borderline Productions.

Séainín recorded 'An Enemy of the People' for BBC Radio 3 last summer. She played the role of ‘Caroline’ in this Henrik Ibsen drama, a new version by Martin Lynch.

'An Enemy of the People' won Best Radio Play at the 2007 Irish Screenwriters and playwrights Guild Awards. The play starred Susan Lynch as Moya McGovern and Séainín playing her daughter Caroline McGovern, alongside Harry Towb, Patrick O’Kane and Charles Lawson.

At the start of 2008, Séainín made the new Crime/Thriller Drama ‘Rush’ playing Dr. Louisa Maxwell. Written by Annie McCartney and directed by Heather Larmour for BBC 7.