McQuarrie was 82 years old when he passed away at his home in Berkeley, California.
The illustrator is best known for designing the look of Lucas' best-known characters, including Darth Vader, Chewbacca, R2-D2 and C-3PO, and also imagined sets for the hit sci-fi franchise.
He also created the alien spaceships in Steven Spielberg's Close Encounters of the Third Kind and E.T., and won an Academy Award in 1985 for Visual Effects in Cocoon.
Lucas, who gave McQuarrie an uncredited role in The Empire Strikes Back, has hailed McQuarrie as a visionary.
He says, "Ralph McQuarrie was the first person I hired to help me envision Star Wars. His genial contribution, in the form of unequaled production paintings, propelled and inspired all of the cast and crew of the original Star Wars trilogy.
"When words could not convey my ideas, I could always point to one of Ralph's fabulous illustrations and say, 'Do it like this.'
"We will all be benefiting from his oeuvre for generations to come. Beyond that, I will always remember him as a kind and patient, and wonderfully talented, friend and collaborator."