During her time in law school, Larkin spent 1974-75 as legislative aide of Rep. Mike Blouin (D—IA-2).
Sanford was a member of the United States Senate Committee on Foreign Relations, and Larkin also worked on the professional staff of the United States Senate Foreign Relations Subcommittee on Near Eastern and South and Central Asian Affairs.
On April 17, 1996, President of the United States Bill Clinton nominated Larkin as Assistant Secretary of State for Legislative Affairs and, after Senate confirmation, Larkin subsequently held this office from July 19, 1996, until January 19, 2001.
In February 2004, Larkin became Vice President (Policy and Advocacy) of CARE, a position she held until September 2008.
In March 2010, she became a senior advisor to the Administrator of the United States Agency for International Development.