The trio of judges appointed to oversee the thorny overcrowding issue extended the deadline to Feb. 28, 2016, but also ordered that inmate numbers be reduced in steps in order to bring the prison population down to 137.5 percent of its official capacity.
California currently has about 117,600 inmates locked up in 34 prisons. The order requires the number to be reduced to 112,164.
California has been under a court order to reduce overcrowding since 2009. Gov. Jerry Brown has fought the order on the grounds he cannot simply release several thousand convicts.
The judge's overseeing the court order said they were reluctant to grant the extension, but agreed to it, in part, because Brown's administration has agreed to end its appeals, the Sacramento Bee said.
Monday's ruling stated that the prison population must be lowered to 143 percent of capacity by June 30 of this year. Failure to meet any of the benchmarks could lead to the federal government ordering the release of low-risk prisoners from a roster compiled by the state, the Los Angeles Times said.
The order also requires the state to "immediately implement" expanded parole programs and adjustments to the early release program proposed last year by Brown. The parole changes include releasing medically incapacitated inmates and those over the age of 60 who have been behind bars for at least 25 years.
The order also prohibited California from increasing the number of inmates lodged at private institutions beyond the current 8,900 individuals.