Authorities said Nathaniel Beller, 29, died just after noon Sunday, the Chicago Sun-Times reported.
Taniya Johnson, 33, died Saturday at a Chicago hospital. The couple's children, Nariya Beller, 4, and Naciere Beller, 9, were in critical condition, said John H. Stroger Hospital spokesman Marisa Kollias.
Nariya was burned over her entire body while Naciere was burned over 35 percent of his body, Kollias said.
The medical examiner's office said the mother also had been stabbed.
Authorities were investigating the fire as arson, the Chicago Tribune reported. Investigators said an accelerant had been poured in the apartment. An empty gasoline can was found behind the building.
Court records indicated Beller had previously been convicted of domestic battery against Johnson.