The shooting happened around midnight at a home in the 2300 block of Binley Drive near Wickersham Lane.
Houston police said all three adults lived in the home.
It's unclear exactly what led up to the shooting, but police said at some point, the suspect got ahold of a gun and opened fire.
Police said the mother was shot three times -- in the face, arm and leg. She was taken to the hospital in stable condition.
The woman's boyfriend, who was in his 50s, was killed, police said.
The suspect was taken into custody, according to HPD. He has reportedly had mental health issues throughout his life.