Previously, Thomas has also served as the Official Opposition critic for Youth and Persons with Disabilities, the Status of Women, and Digital Government.

[5] The report, Hemorrhaging faith: Why and when Canadian young adults are leaving, staying and returning to church was commissioned by the Evangelical Fellowship of Canada and was published in 2012 by Harder and her four co-authors.

A review of the report by Kelvin F. Mutter, an associate professor at McMaster Divinity College, praised it as "a sound piece of research" and "a vital resource for anyone interested in ministering with youth and young adults".

[2][5] In November 2015, she was chosen by interim Conservative leader Rona Ambrose to serve as official opposition critic for Youth and Persons with Disabilities.

[9] On September 1, 2017, Harder, along with fellow Conservative MP Tony Clement, were banned from entering Azerbaijan because they visited the disputed region of Nagorno-Karabakh, which is occupied by Armenia as part an ongoing conflict.

The executive director of the Armenian National Committee of Canada, Sevag Belian, accompanied Harder and Clement and arranged for them to meet senior government officials on their trip.

[19] From February 2019 to August 2020, Harder was the Chair of the House Standing Committee for Access to Information, Privacy and Ethics, as well as its subcommittee on agenda and procedure.

[24] Her environmental positions included ending carbon pricing in Canada, and prohibiting the dumping of sewage in waterways such as the West Coast and the St. Lawrence River.

[24] Harder also cited crime and the opioid crisis as a major issue to be tackled, as well as an advance of aid to local peace officers.

After almost a thousand comments, mostly criticizing her perceived insensitivity to the hundreds dead who had comorbidities, Harder edited her original post to add that it was important to protect the most vulnerable during a pandemic.

[32] According to Timothy Caulfield, the Canada Research Chair in Health Law and Policy at the University of Alberta, Thomas's video incorrectly portrayed science as supporting her claims and was harmful misinformation that could lead to vaccine hesitancy.

[33] In March 2022, Thomas made a statement in the House of Commons defining a dictator as "a ruler with total power over a country, typically one who has obtained control by force" and said that many Canadians agree that such a definition applied to Prime Minister Justin Trudeau.