Judge Thokozile Masipa turned down an application by the prosecutors to refuse bail.
Pistorius could face jail after the judge said the double-amputee Olympian, known as Blade Runner, was “negligent” when he killed law graduate-turned-model Ms Steenkamp, on Valentine’s Day 2013.
The 400m specialist always admitted being responsible for her death at his home in Pretoria, but said he mistook his partner for intruders and fired four bullets from his 9mm pistol through the toilet cubicle.
The judge yesterday dismissed prosecution claims that the double-amputee intentionally killed the 29-year-old, saying Pistorius could not be convicted of either pre-meditated or second-degree murder.
But she returned to court this morning to convict him of culpable homicide - the South African equivalent of the UK’s manslaughter charge - and one gun charge relating to a restaurant shooting.
During a bail hearing after the verdicts, Pistorius’ counsel Barry Roux said his client had complied with previous bail conditions and that there was no reason to remand him into custody ahead of sentencing.
Prosecutor Gerrie Nel said he disagreed, due to the seriousness of the nature and that a custodial sentence was “probable”. He also cited a recent nightclub fracas involving Pistorius and suggestions that the athlete had previously been suicidal.
Mr Roux said the defence disputed the facts of the nightclub incident, and dismissed any suicidal thoughts his client may have.
Judge Masipa said: “I have considered these submissions by counsel.
“The onus is on the state to persuade that it is not in the interests of justice that the bail is extended.
“I grant the application to extend the bail on the same conditions.”
Pistorius will stay with his uncle in Pretoria, where he has lived for the last 18 months since the shooting.
The sentence for a culpable homicide conviction is at the judge’s discretion, although it can range from a suspended jail term and a fine, to up to 15 years in prison.
A sentencing hearing, which could last for three days, will take place on October 13.
Delivering the culpable homicide verdict, judge Masipa told the hushed courtroom: “Having regard to the totality of this evidence in this matter, the unanimous decision of this court is the following: on count one, murder ... the accused found not guilty and is discharged.
“Instead he is found guilty of culpable homicide.”
Yesterday, on the first day of delivering her verdict, the judge criticised Pistorius for acting hastily when he shot Ms Steenkamp.
She said: “If the accused, for example, had awoken in the middle of the night and in darkness seen a silhouette by his bed and in a panic shot at that figure, only to find it was the deceased, his conduct would have been understandable and perhaps excusable.”
She added: “The accused had reasonable time to think, reflect and conduct himself.
“I’m not persuaded that a reasonable person with the same disability would have fired the four shots.
“The accused knew there was a person behind the toilet door, he chose to use a firearm.
“I am of the view the accused acted too hastily and used too much force. It is clear his conduct is negligent.”
Pistorius stood with his hands crossed to hear the final verdict but showed no emotion. The Olympian’s family embraced him during a break in proceedings.
Earlier he was cleared of two gun charges and convicted of a third.
The guilty verdict related to an incident at a restaurant where more than 200 people were present in January last year, although Pistorius denied he was the one to pull the trigger.
Judge Masipa said: “The accused asked for a firearm while in a restaurant full of patrons.
“He may not have intentionally pulled the trigger but that does not absolve him.”
She added: “I view the state has proved beyond all reasonable doubt” that Pistorius contravened gun laws.
Pistorius was found not guilty of illegally being in possession of .38 ammunition. He told the court the bullets belonged to his father and he had them for safe-keeping, although his father refused to make a statement confirming that.
“The state must prove the accused had the necessary mental intention ... to possess a firearm or ammunition before there can be a conviction. It is quite possible to possess a firearm innocently is clear if ... with an intention of returning it to an owner.
“He cannot be found guilty on this count.”
Pistorius was earlier cleared of another gun charge. The incident related to an allegation that the Olympian fired his weapon through a car sunroof in November 2012.
But the judge said prosecution witness Darren Fresco was “poor”, and cleared Pistorius of the charge.
Pistorius denied firing the gun.
The judge said: “The state has failed to establish that the accused is guilty beyond reasonable doubt and has to be acquitted.”
The judge also announced that Darren Fresco, who Pistorius blamed for passing him a loaded gun in the packed restaurant, would not be prosecuted for his part in the incident.
Pistorius made his name by thrilling crowds with his unique sprinting style, having had his legs amputated as a baby and being equipped with prosthetic limbs known as blades.
It was a long wait for a conclusion in the case, the defendant having shot his girlfriend some 18 months earlier.
Interest in the trial was intense, and a ruling that parts of it could be broadcast live on television added to the scrutiny.
It opened on March 3 with a witness describing how she heard “bloodcurdling screams” on the night of the shooting.
But the case was riddled with delays and adjournments, including a lengthy break in proceedings while Pistorius’ mental state was assessed.
The prosecution, led by Mr Nel - nicknamed The Bulldog for his courtroom tenacity - sought to depict the star as having a short fuse and being obsessed with guns.
His defence team, headed by Mr Roux, presented a case that portrayed him as anxious about crime and claimed evidence at the crime scene was mishandled.
Pistorius’ reactions as the case against him was set out ranged from crying during evidence about texts they exchanged and vomiting at a description of her injuries, to calmly taking notes and talking to his lawyers.
It took the judge less than an hour today to deliver the verdicts on the remaining charges, having cleared Pistorius of two murder charges yesterday.
Nathi Mncube, for the National Prosecuting Authority, said they were “disappointed” Pistorius was convicted of only two charges.
Speaking outside the court he said: “We respect the judgment that has been delivered.
“We believed in this instance there was enough evidence to secure a conviction under pre-meditated murder.
“Of course we are disappointed. We are disappointed we did not secure a conviction under pre-meditated murder and also there was acquittal on the other two (gun) charges.
“The matter has not been concluded yet, we are still waiting for a sentence to be imposed.”
He said it was too early to decide whether prosecutors would launch any appeal.
Pistorius made no comment as he left the court building and was bundled into a waiting car.
He was accompanied by several security officers, as hordes of journalists and members of the public clutching camera phones tried to catch a glimpse of the athlete.