In the 1980's, Mackenzie wrote vignettes for Sesame Street (1969) for several years.
Mackenzie was chosen to play the recurring character, Greg Hearney, on the TV series The Net (1998) after he made a crazy videotape in which he played 15 different characters in a minute and a half, through digital editing and sent it to the producers of the TV series. The producers had stated they were looking for someone with 'versatility'.
Mackenzie has British and Canadian citizenship.
His height is 6' (1.83 m).