The Old Bailey was due to reopen on Monday following emergency work to restore power after an electrical fire inside the high-security building.
The Central Criminal Court was shut, disrupting dozens of cases, after a fire broke out last Wednesday morning in an electrical substation.
Black smoke spewed from the building, courtrooms were plunged into darkness, 1,500 people were evacuated and two had to be rescued from lifts.
Four fire engines and 25 firefighters were called as crowds of barristers in black gowns and wigs gathered at the front of the building.
Defendants were seen being escorted by police out of a side exit and into waiting prison vans to be returned to jail.
Among the cases affected were the ongoing trial of Constance Marten and Mark Gordon, who are accused of the manslaughter of their baby daughter, and the inquest into the deaths of the victims of the Reading terror attack.
London Fire Brigade said the cause of the fire was “accidental” and not being treated as suspicious.
On Friday, Judge Mark Lucraft KC, the Recorder of London, said the building would reopen at noon on Monday following emergency works to restore power.
He said various health and safety checks were needed before normal business could resume.
The Old Bailey is the world’s most famous criminal court and has high levels of security as it hears major criminal cases, including murder and terrorism trials.
In the past, it has been identified as a high-value terror target and was badly damaged in an IRA car bomb attack in 1973.