She is best known for playing the roles of Sandy in Grease and Elle Woods in Legally Blonde the Musical in London's West End and being a member of Celtic Woman from 2012 to 2018.

As a result, she played the lead female role of Sandy in the West End production of Grease with Danny Bayne beginning in August 2007.

[1] McFadden sang with Ben Morris and Séan Carey in the final of RTÉ One's Fame: The Musical in Dublin on Sunday 13 June 2010.

On 5 January 2012, McFadden was named as a replacement for Lisa Kelly, then going on maternity leave, in the all-female ensemble Celtic Woman.

After Kelly announced her departure from the group was permanent in January 2013, McFadden became a full-time member of Celtic Woman.

In October 2019, Susan rejoined Celtic Woman for a few shows filling in for Mairéad Carlin while she recovered from appendicitis.