The sentencing was the first time prosecutors confirmed Watts' motive: to begin a new life with his girlfriend who he had been seeing for months before he carried out the crimes.
Watts murdered his wife and children on August 13, 2018. He placed his daughters in oil tanks and wife, who was 15 weeks pregnant, was found in a shallow grave.
Before a judge handed down his sentence on Monday, Watts listened to his father-in-law and brother-in-law deliver statements about him.
They dubbed him an "evil monster" and asked why he "slaughtered" his family who worshiped him.
Mr Watts did not speak at the hearing, but his lawyers said: "Mr Watts has asked us to share this morning that he is devastated by all of this and although he understands that words are hollow at this point, he is sincerely sorry for all of this."
Watt's mother also spoke at the sentencing.
She said through tears, "My name is Cindy Watts. I am the grandmother of two beautiful granddaughters and I am the mother of Christopher Watts.
"To my son Christopher. I have known you since the day you were born into this world. I've watched you grow from a quiet and sweet, curious child, who Bella reminded me so much of, to a young man who worked hard in sports and later in mechanics to achieve your goals.
"You were a good friend, father, brother and son. We have loved you from the beginning and we still love you now.
"This might be hard for some to understand how I can sit here under these circumstances and tell you all that we are heartbroken. Although we can't imagine what could have led us to this day, we love you.
"Maybe you can't believe it either. As the lord said, I have loved you with an everlasting love. Therefore I have continued my faithfulness to you.
'As your mother, Chris, I have always loved you. I still do."