Feltman joined the United States Foreign Service in 1986, serving his first tour as consular officer in Port-au-Prince, Haiti. He served as an economic officer at the U.S. Embassy in Hungary from 1988 to 1991. From 1991 to 1993, Feltman served in the office of the Deputy Secretary of State, Lawrence Eagleburger as a special assistant concentrating on the coordination of U.S. assistance to Eastern and Central Europe.[5]
After a year of Arabic studies at the University of Jordan in Amman, Feltman served in the U.S. Embassy in Tel Aviv from 1995 to 1998, covering economic issues in the Gaza Strip. From 1998 to 2000, Feltman served as chief of the political and economic section at the U.S. Embassy in Tunisia. He served in Embassy Tel Aviv as Ambassador Martin Indyk's special assistant on peace process issues from 2000 to 2001. He then moved to the U.S. Consulate General in Jerusalem, where he served first as deputy from August 2001 to November 2002) and then as acting principal officer from November 2002 to December 2003.
Feltman served as the assistant secretary of state for Near Eastern affairs from August 2009 to June 2012 with the rank of career minister, before taking his post at the United Nations. In June 2012 he was appointed under-secretary-general for political affairs, a position he held until April 2018.
In September 2017, Feltman announced his support for Palestinian statehood, stating "Economic development, critical as it is, is no substitute for sovereignty and statehood."[6]