After studying law and completing his legal traineeship in Cologne, Berndt Hess was admitted to the bar in 1994. He gained his first professional experience at a Cologne law firm focused on civil and business law matters.

In 1996, he moved to the Frankfurt office of international law firm Clifford Chance, initially as an associate and, from 2000, as a partner. There, his practice focused on general business law, German and European antitrust law, dispute resolution, and, increasingly from 2010 onward, advising companies on compliance matters.

From 2014 to 2017, Berndt Hess headed the group-wide antitrust compliance at Bilfinger SE and also served as Compliance Officer for several divisions of the group. During this period, the company was reviewed by a compliance monitor appointed by the U.S. Department of Justice.

Since May 2017, Berndt Hess has been practicing as an attorney in his own law firm.

Berndt Hess is a member of the Studienvereinigung Kartellrecht and the Kartellrechtsforum Frankfurt.