Spears' latest single has gone to number one in the US
Britney Spears' father is to maintain indefinite control of the pop star's personal and financial affairs.
James Spears was granted control of his daughter's assets in February after she was admitted to a psychiatric ward.
The arrangement was due to expire on 31 December, but Los Angeles Superior Court Commissioner Reza Goetz has now agreed to make it permanent.
Ms Spears had the situation explained to her and chose not to oppose it, a court-appointed lawyer said.
The 26-year-old could petition later to have the conservatorship removed, but the court's order otherwise constitutes a lifetime arrangement, a court information officer said.
Lawyers for James Spears declined to comment after the hearing.
The move may come as a surprise to the pop star's fans, as she has recently seemed to be on the mend - appearing lucid and in control at an MTV awards show and showcasing a new slimline look in the video for her latest single, Womanizer.
But Ms Goetz said she had granted permanent conservatorship based on recent medical evaluations and lawyers' recommendations, which showed the singer was "susceptible to undue influence."
She added that the ruling was "necessary and appropriate" given the complexity of Ms Spears' financial situation.
One advantage of the ruling, as far as the pop star is concerned, is that it shields her from some legal action.
At her recent trial for driving without a valid licence, James Spears testified on his daughter's behalf, and refused to allow her to take the witness stand.
An outstanding trial, in which a former manager is suing the pop star for unpaid earnings, has also been delayed as Ms Spears has been deemed unfit to give sworn testimony.