The decision means the sentencing phase of his trial, now set to begin on Wednesday, can go ahead.
The self-described white supremacist was convicted in December for crimes connected to the racially motivated killing of nine African-American parishioners in the Emanuel AME Church in downtown Charleston.
He attended a Bible study in the basement of the historic black church known as “Mother Emanuel” on June 17, 2015 before producing a handgun and killing his victims, aged 26 to 87 years old.
Roof, 22, was first declared competent to stand trial by US District Judge Richard Gergel in November following a previous hearing closed to the public. Roof then chose to represent himself during jury selection of his trial, a strategy Gergel deemed “unwise. “
Roof participated passively in jury selection, then reinstated his lawyers as the prosecution sought to establish his guilt during trial.
However, his main defense attorney, the renowned death penalty expert David Bruck, called no witnesses of his own and did not significantly challenge any of the government’s witnesses, who included two survivors, one of them a woman who watched Roof execute her adult son before her eyes.
After being convicted of all 33 charges against him in December, Roof indicated he would again like to represent himself during the sentencing phase of the trial.
He has told the judge he does not plan to introduce any evidence or witnesses on his behalf, including any evidence of his mental health.
In his closing argument, Bruck said Roof had no real friends and is unable to make small talk. He noted that beyond Roof taking many photographs of himself with a gun and Confederate flag before committing his crimes, he also took hundreds of pictures of his cat.
During the sentencing portion of the trial, the jury will possibly hear testimony from dozens of witnesses called by the government, including relatives of the victims.
They may also hear from Roof himself, who has said he will make opening and closing statements during the next portion of the trial.
Other charges against Roof included hate crimes resulting in an attempt to kill; obstruction of exercise of religion resulting in death or an attempt to kill; and assorted firearms charges with the intent to commit murder or a violent crime.
Roof is also facing state murder charges in South Carolina, although that trial is not due to begin until January 17. State prosecutors also are seeking the death penalty.