Mariana Tavares joined the Portuguese Competition Authority (PCA) in September 2004, where she has been the Director of the International Relations Bureau, since November 2008. She was a member of the Working Group for the Revision of the Portuguese Competition Act, a multilateral working group composed of 8 people, created in September 2011 by the Ministry of the Economy and Employment. This group that included representatives of the Government, Bar Association, International Chamber of Commerce and PCA was responsible for the discussion of the revision of the Portuguese Competition Act and the bill that was subject to public consultation. She was also tasked with drafting the reform of the Competition Authorities Leniency Guideline that should enter into force in the last trimester of 2012.
Before her current position, she served as a Legal Advisor to the Board of the Portuguese Competition Authority between December 2007 and October 2008. Earlier in her career at the Portuguese Competition Authority, she was a case handler in the Restrictive Practices Department.