Judge Thokozile Masipa dismissed an application by Pistorius' defence lawyers to challenge the appeal by prosecutors, who were last year granted permission by Masipa to have Pistorius' negligent killing conviction reviewed. Prosecutors want Pistorius found guilty of the more serious charge of murder for shooting Steenkamp multiple times through a door in a bathroom in his home in 2013.
A murder conviction would call for a minimum sentence of 15 years in jail.
The 28-year-old Pistorius is currently serving a five-year prison sentence for culpable homicide, which is comparable to manslaughter. He could be released from jail in August to serve the remainder under house arrest.
"The order that I grant in this matter is to strike off the application," the black-robed Masipa said in her ruling on Friday, dismissing the defence's application.
The ruling means Pistorius' case looks set to go to South Africa's Supreme Court of Appeal, where a panel of judges would decide if Masipa's initial verdict to acquit Pistorius of murder at the end of the seven-month trial last year was wrong.
In December, Masipa granted prosecutors permission to take the case to the Supreme Court of Appeal and challenge her own ruling. Pistorius' lawyers were arguing Friday that Masipa should not have allowed the appeal.
Masipa made her latest ruling after a short court session in Johannesburg. Pistorius' trial was held in another courthouse in the capital Pretoria. The Olympian and multiple Paralympic champion is in a Pretoria prison and did not attend Friday's proceedings. There were also no members of his or Steenkamp's family present.
Masipa heard arguments by Barry Roux, Pistorius' chief defence lawyer at trial, and Gerrie Nel, the chief prosecutor.
Roux argued prosecutors had "mistakenly" been given permission to appeal. Nel said there was no basis for this application by Pistorius' defence, which wanted a "never-ending case" to prevent it from going to the appeal court.
The Supreme Court of Appeal sits in the central city of Bloemfontein. No date has been given for the appeal but cases can sometimes take two years to reach the court, legal experts say.
The mother of Pistorius' slain girlfriend, who attended much of last year's trial, said this week that she was not interested in the appeal.
"How is it going to help me?" June Steenkamp said, adding "my daughter died. Horribly."Suggest a correction