Piirimäe researched Estonian history under the Swedish Empire in the 17th century, but also the Enlightenment in the 18th century, especially the French Revolution.
Helmut Piirimäe was married to art historian Krista Piirimäe. They have three sons and a daughter.
- ERR (21 August 2017). "Historian Helmut Piirimäe dies at 86". Retrieved 24 August 2017.
- Helmut Piirimäe's publications (in Estonian)