Truszczynski's research interests include knowledge representation, nonmonotonic reasoning, logic programming, and constraint satisfaction and programming. He is the author or co-author of over 170 technical papers in journals, conference proceedings and books. Jointly with Victor Marek he wrote a research monograph "Nonmonotonic Logic" on mathematical foundations of nonmonotonic reasoning, which marked a milestone in the development of the field.

His paper Stable Logic Programming, also a joint work with Victor Marek, helped launch the field of answer-set programming. Truszczynski was also a co-editor of the book "The Logic Programming Paradigm: a 25-Year Perspective", celebrating accomplishments of the field of logic programming, and of several conference proceedings, including Proceedings of International Conference on Logic Programming, ICLP 2006, and Proceedings of the International Conference on Knowledge Representation and Reasoning, KR 2010. In 2011, jointly with Gerd Brewka and Victor Marek, he edited a volume "Nonmonotonic Reasoning at 30" of invited papers assessing advances in nonmonotonic reasoning 30 years after the field had been established.

Truszczynski is active in his research community. He was an organizer or the program committee chair for several major conferences in his field. He served on the Executive Committee of the Association of Logic Programming (2003-2008), and as Chair of the Steering Committee of Nonmonotonic Reasoning Workshops (2000 - 2008). Since 2000, he has served on the Steering Committee of Knowledge Representation, Inc. and, since 2010, is its President. He also serves on editorial and advisory boards of several professional journals, including Journal of Artificial Intelligence Research, Theory and Practice of Logic Programming and AI Communications.