The jury found Balfour of all seven counts he faced.
If Balfour was convicted on two or more counts of murder it would mean mandatory life without parole per Illinois law.
Prosecutors presented 11 days of testimony and called 83 witnesses, starting with Jennifer Hudson. Friday was the third day of deliberations.
Jennifer Hudson was the first witness called and attended every day of testimony in the trial. The Hudson family was in the courtroom Friday when the verdict was read.
Balfour was charged with three counts of first degree murder, one count of home invasion, one count aggravated kidnapping, one count residential burglary, and one count possession of a stolen motor vehicle.
The prosecution said Balfour acted out in jealousy because his estranged wife, Jennifer Hudson's sister Julia, was seeing someone else.
Balfour's defense team said there was no physical or DNA evidence and suggested police should look at other suspects, like people associated with Jennifer Hudson's brother Jason, a known drug dealer.
The jury was sequestered in a hotel and their identities have been kept secret.