Judge Robert Perry determined that with time served and good conduct, Mehserle should be released Monday.
Mehserle was convicted in July 2010 and sentenced in November 2010 to two years in prison for involuntary manslaughter of Oscar Grant.
According to the Superior Court of California, Mehserle will have served 365 days in custody by Sunday, June 12, 2011. With good-conduct credits, Mehserle's total custody amounts to 731 days served, equaling the sentence imposed.
Mehserle and his partner were responding to an unruly crowd on a BART platform in Oakland on New Year's Day 2009.
While attempting to subdue Grant, who was unarmed, Mehserle fatally shot Grant in the chest. Mehserle said he was intending to use his Taser, not his firearm.
The case, which inflamed racial tensions in the Bay Area and sparked violent protests, was moved prosecuted in Los Angeles due to pre-trial publicity.
Supporters and family of Grant met at the Southern California Library in South Los Angeles on Saturday afternoon for an emergency meeting held by the Los Angeles Coalition for Justice for Oscar Grant.
"It's painful to us as a family," said Cephus Johnson, Grant's uncle, of the pending release of Mehserle. "There was no accountability. There was no justice in that courtroom."
Critics say Mehserle is receiving preferential treatment.
"He was sentenced to state prison and he never set a foot outside Los Angeles County jail," said Jubilee Shine, a member of the coalition. "He did a country club bid. He did less than half of the time Michael Vick served for abusing some animals, so it's a perversion of justice."
Grant's supporters said they plan to rally in front of the U.S. attorney's offices in Oakland and Los Angeles when Mehserle is released early Monday morning
"He's going to live with what he did and he's going to suffer from that, but our ultimate goal is to contact the Department of Justice and assist upon them bringing criminal charges for civil rights violations," Johnson said.