Dahl was a professor of computer science at the University of Oslo and is considered to be one of the fathers of Simula and object-oriented programming along with Kristen Nygaard.

As his career advanced, Dahl grew increasingly interested in the use of formal methods, to rigorously reason about object-orientation for example.

[4] Dahl and Nygaard were the first to develop the concepts of class, subclass (allowing implicit information hiding), inheritance, dynamic object creation, etc., all important aspects of the OO paradigm.

The object-oriented approach is now pervasive in modern software development, including widely used imperative programming languages such as C++ and Java.

He received the 2002 Institute of Electrical and Electronics Engineers (IEEE) John von Neumann Medal (with Kristen Nygaard)[5] and was named Commander of the Royal Norwegian Order of St. Olav in 2000.