Bobby Woods, 21, was convicted Friday of capital murder in the 2015 death of Mason Cuttler.
Investigators said Woods told police that his girlfriend Billie Jean Cuttler was pregnant and that he killed the boy because he wanted to make room in his home, which housed three families at the time.
A lawyer said Cuttler wasn't pregnant.
Woods told police he pushed the toddler into a pond near Lufkin, 110 miles northeast of Houston, turned his back and let him drown.
His body was found Aug. 18, 2015, a day after he was reported missing. Cutter pleaded guilty to conspiracy to commit murder in exchange for a 20-year prison sentence.
The Associated Press contributed to this report.