In 2013 he returned to physics research as an associate member of the Institute for Quantum Computing (IQC) at the University of Waterloo.

He is an honorary fellow of Norman Bethune College at York University and president of the board of directors for the Mont Megantic Observatory project.

In 1983, he became a visiting scholar at Stanford University under Nobel Prize laureate Arthur Leonard Schawlow.

He is a laser-physicist, and his research has included work on electro-optics, laser-induced fluorescence of particles and crystals and multi-photon laser spectroscopy.

From October 22 to November 1, 1992, MacLean flew onboard Space Shuttle Columbia as a payload specialist for Mission STS-52.

On September 13, he performed his first spacewalk, a 7-hour EVA to activate the solar panels on the P3/4 truss – the second Canadian to do so, after Chris Hadfield.