Upon retirement, Athans moved to Lisbon, Portugal, where he was an Invited Research Professor in the Institute for Systems and Robotics, Instituto Superior Técnico where he received a honoris causa doctorate from the Universidade Técnica de Lisboa in 2011.
[citation needed] From 1961 to 1964, Athans was employed as a member of the technical staff at the MIT Lincoln Laboratory, Lexington, Mass.
From 1964, until his early retirement in 1998, he was a faculty member in the MIT Electrical Engineering and Computer Sciences department, where he held the rank of Professor.
In 1995 he was visiting professor in the Department of Electrical and Computer Engineering at the National Technical University of Athens, Greece.
From 1997 to 2011 he was an Invited Research Professor in the Institute for Systems and Robotics, Instituto Superior Técnico, Lisbon, Portugal.
His last research interests focused on dynamic models of the human immune system and robust adaptive control methodologies.
He was the recipient of a Polish Academy of Sciences Medal, “For contributions to Control Theory” in Warsaw, Poland, on June 30, 2005.