Pistorius' agent, Peet van Zyl, told The Associated Press that he cancelled the contract on Saturday for a high-profile rematch next month with fellow double-amputee Alan Oliveira to promote the 2016 Rio Olympics and Paralympics.
Oliveira, who beat Pistorius in the 200 meters at the Paralympics in London last year, and Pistorius were to run a straight 200 on Copacabana beach in Rio de Janeiro on March 31.
Pistorius was charged with the murder of Steenkamp after she was shot dead at the home of the multiple Paralympic champion on Thursday. South African prosecutors have said they will pursue a more serious premeditated murder charge against the 26-year-old Pistorius, leaving him possibly facing a life sentence.
"I can't plan anything," Van Zyl said of Pistorius' immediate running career, which was not a priority after the murder charge and Steenkamp's death. "I will only have him run when he is in a condition to run as a world-class athlete. Physically and mentally fit."
Pistorius broke down and wept on his first appearance in court on Friday, while his family said on Saturday in a statement to the AP that they were "devastated" and in "a state of total shock."
Pistorius' uncle, Arnold Pistorius, said they were also grieving for Steenkamp, her family and her friends.
Van Zyl said he had first cancelled two races in Australia, in Sydney on March 9 and Perth on March 16, which were to start Pistorius' season as he aimed to qualify for the world championships in Moscow in August and build on his historic runs on his carbon-fiber blades at the London Olympics.
A 150-meter race in May against Britain's Jonnie Peacock, the single-amputee sprinter and 100-meter Paralympic champion, also had to be called off, as well as scheduled Diamond League appearances and a race at the Drake Relays in Iowa in the United States.
Pistorius and his longtime coach Ampie Louw planned to give up track together after the next Olympics and Paralympics in Rio but it was uncertain if Pistorius will ever compete at the highest level again, having made history as the first amputee athlete to run at the able-bodied worlds in 2011 and then the Olympics last year.
In all, Van Zyl said he had canceled around seven 400-meter races, as well as the exhibitions against Oliveira and Peacock.