[1] He formulated the model–view–controller (MVC) pattern for graphical user interface (GUI) software design in 1979 while visiting the Xerox Palo Alto Research Center (PARC).

Reenskaug described his early Smalltalk and object-oriented programming conceptual efforts as follows:[2] MVC was conceived as a general solution to the problem of users controlling a large and complex data set.

He founded the information technology company Taskon in 1986, which developed tools based on OOram.

The OOram ideas matured and evolved substantially into the BabyUML project, which culminated in creating the data, context and interaction (DCI) paradigm.

Reenskaug wrote the book Working With Objects: The OOram Software Engineering Method with co-authors Per Wold and Odd Arild Lehne.