Lenarčič entered the Slovenian foreign service in 1992 . His first posting in 1994-1999 was at the Mission of Slovenia to the United Nations in New York.[1][2]
From 2000 to 2001 Lenarčič worked as adviser to the foreign minister and Prime MinisterJanez Drnovšek. From 2002 to 2003 he served as secretary of state in the office of the prime minister.[1][2]
Lenarčič was ambassador of Slovenia to the Organization for Security and Co-operation in Europe (OSCE) in Vienna from 2003 to 2006, and chaired the OSCE Permanent Council in 2005 during the Slovenian chairmanship.[1][2]
From 2006 to 2008 Lenarčič was secretary of state for European affairs, including representing Slovenia during the Lisbon Treaty negotiations in 2007 and later representing the Slovenian EU Council Presidency to the European Parliament in 2008.[2]
In early March 2020, Lenarčič was appointed by von der Leyen to serve on the Commission's special task force to coordinate the European Union's response to the COVID-19 pandemic.[4]