Siddiqi served the Aligarh Muslim University in different capacities between 1965 and 1998 such as Professor of Applied Mathematics and Chairman Department of Mathematics, Provost of a Prestigious Hall of Residence, Member-in-Charge AMU Press, Dean of the Faculty of Science, Chief Election Officer of the AMU and AMU
students' union. He had held visiting assignments in different parts of the world including USA, Canada, Germany, Iran, Algeria, Saudi Arabia, Oman and Malaysia. From December 1973 to August 1975 Siddiqi was
visiting professor at the
University of Tabriz, Iran. From October 1980 to April 1983 he was visiting professor at Constantine University,
Algeria. From October 1998 to April 2007 Siddiqi was employed as Professor of Mathematics at the
King Fahd University of Petroleum and Minerals, Saudi Arabia. Siddiqi had also served
Gautam Buddha University from 15 October 2011 to 9 January 2013 and contributed significantly to its development. ==Fellowships==