Jurors in federal court deliberated for a week before convicting 38-year-old Kaboni Savage on Monday.
Prosecutors are seeking the death penalty, and penalty phase deliberations are scheduled to begin Monday.
Authorities said that although Savage has mostly been in prison since 2003, he gave orders through phone calls and prison visits and communicated with other inmates through prison plumbing pipes.
His 30-year-old sister, Kidada, was convicted of all counts in connection with the firebombing and faces life in prison.
Savage, a former boxer who has denied any role in the attacks, is currently serving a 30-year drug-trafficking sentence.