During the COVID-19 pandemic, McCartney contributed content to academic journals and broadcasting platforms, personal blog, and social media to inform the public and dispel myths about coronavirus disease.

[8][9][10] McCartney started popular science writing after reading a misleading newspaper article claiming health benefits associated with CT scanning.

[12][13] She has written and hosted her own radio shows, including Farewell Doctor Finlay and Tell Me Where It Hurts, which looked at historical and contemporary GP practise in the National Health Service.

[17] McCartney established the Royal College of General Practitioners working group on overdiagnosis, which she defined as "the application of diagnoses and treatments for patients that are of little or no value".

[25] As part of her campaigning efforts, she contacted the Advertising Standards Authority, who upheld her complaints on the use of misleading information and non-evidence based inspections.

[24] In 2016 McCartney joined Phil Hammond for a month long show at the Edinburgh Festival Fringe, where the pair urged the audience to protect the National Health Service from "market mayhem".

That it has taken a global crisis, which is killing patients and health-care staff, and which will have profound psychological sequelae, to make this happen, is catastrophic, and an unpayable price”.

[31] She is a patron of HealthWatch UK, a charity which challenges poor evidence in health reporting, as well as an honorary fellow of the Centre for Evidence-Based Medicine.