The most popular running route in Marrakech (and one of the better options for a longer length run) is a simple straight shot along Boulevard Mohamed VI. This 8 km (one way) street runs diagonally across the city, from P2006 in Champ El Ghoul in the north to P2017 in Agdal in the south.
A wide stone paved walkway lines the centre median for the entirety of the boulevard, featuring gardens, fountains, and palm trees. There are also sidewalks on either side of the road, which is relatively lightly trafficked.
While the full course is close to 11km, this is an out & back so you’re free to choose the length of your run.