Defence lawyer Barry Roux asked Pistorius to remove his prostheses, and the former track star and Olympian, who had taken off his suit and put on a T-shirt and shorts during a recess, walked in front of Judge Thokozile Masipa.
The demonstration drew gasps from some onlookers in the courtroom and Pistorius became tearful.
“I don’t want to overplay disability,” Mr Roux said ahead of the demonstration, “but the time has come that we must just look [at Pistorius] with different eyes.”
Judge Masipa will deliver Pistorius’s sentence after hearings end this week.
Pistorius is currently under house arrest and awaiting a new sentence after an appeals court overturned an initial manslaughter conviction against him and changed that to murder for shooting Ms Steenkamp at his home in 2013.
South Africa has a minimum sentence of 15 years in prison for murder, although a judge can reduce that in some circumstances.
Walking in court without his prosthetic legs, Pistorius was unsteady at times, holding on to wooden desks and helped by a woman at one point. He then returned to a bench where he sat alone, head bowed, and wiped away tears.
When he had his chance to address the judge, chief prosecutor Gerrie Nel asked Judge Masipa not to forget that Pistorius shot four times into a toilet cubicle from close range with no justification when he killed Ms Steenkamp.
“Pity will play no role in the sentence,” he said.
The defence’s argument is that Pistorius, a multiple Paralympic champion and a history-making amputee athlete who ran at the 2012 Olympics, was a scared disabled man when he shot Ms Steenkamp through the toilet door.
Pistorius was not wearing his prosthetic legs when he fired the fatal shots; he testified at his murder trial that he felt vulnerable and thought an intruder was in the house.
Mr Roux said on Wednesday: “It was not the man winning gold medals that must be judged” but rather “a man standing on his stumps at 3 o’clock in the morning in the dark that must be judged”.