A Criminal Court jury in Bradley County on Friday found Aaron Lawson guilty on all counts, including two charges of first-degree murder.
The convictions carry an automatic life prison sentence.
Lawson took the witness stand to say he was acting in self-defense in the 2011 slayings of Eddie and Debbie Phillips, who were shot three times each outside their Cleveland home.
He said he was fed up with hostility between his family and the Phillips family. The couple had been involved in a custody battle over their 14-year-old granddaughter.
A sentencing hearing will be March 24.