Patrick Haney Jr., 29, could face the death penalty if convicted of first-degree murder in Fayette County in the September 2011 death of Trenton St. Clair.
The selection of jurors and alternates was completed Friday for the trial.
The child's mother, 30-year-old Heather Forsythe, of Point Marion, pleaded guilty last week to endangering the welfare of a child.
Prosecutors allege that Haney systematically beat the boy over several weeks and that his mother knew about the abuse but did nothing to stop it.
They have recommended a sentence of 2 1/2 to five years for Forsythe, who is scheduled to testify in Haney's trial.