Mr Abu Kassim began his career as Investigation Officer at the Malaysian Anti-Corruption Agency (ACA) in 1984. He made his way up to the Director of the Planning and Policy Coordination Division in 1999, and the Director of ACA for the states of Perak and Penang respectively in 2000 and 2003. He was appointed Director of the Malaysian Anti Corruption Academy (MACA) in 2005; Chief Integrity Officer at Amanah Raya Berhad in March 2006, and Deputy Director General I of ACA in 2007. Mr Abu Kassim took responsibility as Deputy Chief Commissioner of the Malaysian Anti-Corruption Commission (MACC) in 2009, and was appointed Chief Commissioner of MACC on 1 January 2010.

He has been a member of the Interpol Group of Experts on Corruption since 1997, and is a member of the Executive Committee of International Association of Anti-Corruption Authorities. He presented numerous working papers relating to the fight against corruption, inter alia "The Fight Against Corruption: A Collaborative Approach Between MACC and MACA in Combating Corruption" which was introduced at the 78^th Interpol General Assembly Session in Singapore in 2009.

Mr Abu Kassim is currently an Adjunct Professor to the Education and Social Sciences Faculty at the University Industry Selangor. He is also a member of the International Academic Advisory Board of the International Anti-Corruption Academy of Vienna; the Board of Director of the Institute Integrity of Malaysia, and the Advisory Panel for Malaysia Company Commission Training Academy.