The 47-year-old was hit by a car near Gawler about 7am on Wednesday and died at the scene, while the driver was not injured but taken to hospital as a precaution.
Modra, a swimmer and tandem cyclist, won five gold and five bronze medals at eight Paralympic Games.
According to Paralympics Australia, Modra’s career has spanned three decades.
“Making his Paralympic debut in 1988, Kieran represented Australia in athletics, placing sixth in javelin behind Rio 2016 teammate and gold medallist Russel Short,” the website said.
"Swimming to aid his recovery from a knee injury, Kieran became so good that he was selected to compete at the 1992 Paralympic Games in Barcelona, where he won bronze in the 100m and 200m backstroke.”
Paralympics Australia said Modra started cycling competitively in 1995 and won his first gold the following year.
“His talents are not restricted to sport, also gifted in tatting, crocheting, and movie editing,” Paralympics Australia says.