Prior to being elected, she worked as a journalist in national newspapers for more than 20 years.

[1] From 2010 to 2016 she sat on the Children's Panel for the East End of Glasgow.

Mackay worked as a Parliamentary Assistant to Gil Paterson, the former SNP MSP for Milngavie and Clydebank, before being elected in May 2016.

[3] She was Deputy Convenor of the Justice Committee in Session 5, was on the Education Committee and convened a number of Cross Party Groups.. At the Scottish Parliamentary election in May 2021, Mackay was re-elected with a majority of 11,484 (3,384 increase from 2016).

[4] In Session 6, she is a member of the Scottish Parliament's Criminal Justice Committee, a member of the Animal Welfare, Chronic Pain (Co-Convenor), Women’s Justice (Convenor), Fair Trade, Men's Violence Against Women and Children, Prevention and Healing of Adverse Childhood Experiences and is a Senior Party Whip.