With the ruling handed down Friday, jury selection in the murder trial is set to begin Monday.
Roof, 22, faces 33 federal charges in the massacre at the Emanuel African Methodist Episcopal Church, which occurred during a Bible study group meeting. He faces the death penalty.
On June 17, Roof walked into the church and sat in the Bible study session for nearly an hour before drawing a semi-automatic handgun.
Friends said he was obsessed with the riots in Ferguson, Missouri, and the Trayvon Martin case, and was said to be in favor of segregation.
Roof reportedly spewed insults at his victims while shooting, and left three people alive to tell others his motive was that he hated black people.
Killed in the shooting were Rev. Clementa Pinckney, Rev. Daniel Simmons Sr. , Rev. Sharonda Singleton, Rev. DePayne Middleton-Doctor, Cynthia Hurd, Ethel Lance, Susie Jackson, Myra Thompson and Tywanza Sanders.