Speaking at the University of Notre Dame, Thomas said judges "venturing into areas we should not have entered into" is part of why the nomination process, particularly for federal judges with lifetime appointments like himself, is so contentious.
"The court was thought to be the least dangerous branch and we may have become the most dangerous," Thomas said. "And I think that's problematic."
He did not cite any specific examples.
Thomas is the most senior justice on a court that grew more conservative under President Donald Trump, who placed three justices on the court. His speech Thursday is at the alma mater of his newest colleague on the court, Amy Coney Barrett, who graduated from Notre Dame Law School and served on the faculty there.