Harri Tapio Tiesmaa started as a district prosecutor at the Helsinki Prosecutor's Office in 1991, and has worked as a specialist prosecutor of financial crime since 1999. He worked as a seconded national expert at Eurojust in 2009–2010. He was appointed as National Member for Finland at Eurojust in July 2011, before returning to his own post in August 2015.

Tiesmaa is a member of the European Judicial Cybercrime Network (EJCN). He also chaired Eurojust’s Cybercrime Task Force in 2014 and 2015.