Martin Sunnqvist's research focuses on comparative legal history, with a specific emphasis on the history of constitutional law and procedural law. His doctoral thesis examined the history of judicial review of legislation in the Nordic countries. Currently, Martin Sunnqvist is conducting research on the rule of law in Europe, as well as exploring the topics of judicial independence and impartiality.

In addition to his academic pursuits, Martin Sunnqvist has practical experience as a judge, having served as a district judge at Malmö City Court for five years. He has also been appointed to investigate the legal framework surrounding the Swedish royal family and the royal household.

Furthermore, Martin Sunnqvist is engaged in the study of heraldry and symbols, and he serves as a member of the Heraldic Committee of the Swedish National Archives.

His teaching activities primarily revolve around Swedish and comparative legal history, as well as civil procedural law.