For nineteen years, she taught business studies at West Lothian College, where she was an active member of the Educational Institute of Scotland (EIS) trade union.

[6] In 2007, Fellows unsuccessfully contested the Motherwell and Wishaw Scottish Parliament constituency against the incumbent, then-First Minister of Scotland Jack McConnell,[7] and then in 2010 unsuccessfully contested the Motherwell and Wishaw United Kingdom Parliament constituency, losing to the incumbent Frank Roy.

[2] Fellows was re-elected as MP for the seat at the 2017 UK General Election, with a significantly decreased majority of 318 votes.

In June 2017, she was appointed the SNP spokesperson for Small Business, Enterprise and Innovation, a post she held until January 2020.

[2] In the 2024 UK general election, she contested the new seat of Motherwell, Wishaw and Carluke but was unseated by Pamela Nash.