Michael Riley, 37, was found guilty in the December 2006 death of daughter Rebecca. The jury had begun deliberating his case Thursday afternoon. He faces an automatic sentence of life in prison without parole.
His wife, Carolyn, was convicted of second-degree murder last month. Her mandatory life sentence allows for parole after 15 years.
"It's a very difficult decision. I'm going to look at it and file an appeal," defense attorney John Darrell told The Associated Press.
The Rileys were accused of giving their daughter a fatal overdose of Clonidine, which she was taking for attention-deficit hyperactivity and bipolar disorders. Defense attorneys said Rebecca died of pneumonia and blamed the overdose on lax monitoring by a psychiatrist who had prescribed the medication.
Assistant District Attorney Frank Middleton told the jurors in closing arguments that Michael Riley either gave Rebecca the extra pills himself or told his wife to do so.
"He knows it's going to shut her up, and shut her up for good," Middleton said.
Middleton said Riley was a cold-hearted father who made up symptoms of mental illness in Rebecca and his two other children so he could collect Social Security disability benefits for them. The defense said Riley was trying to take care of his family while struggling with problems of his own, including bipolar disorder.
Michael Riley repeatedly ordered his wife to increase Rebecca's dose of Clonidine, the prosecutor said, to keep her quiet and out of his way. The night she died, she was given two to three times her daily dose, Middleton said.
A state medical examiner found that Rebecca died of the combined effects of Clonidine; Depakote, an anti-seizure and mood-stabilizing drug prescribed for bipolar disorder; and two over-the-counter drugs, a cough suppressant and an antihistamine. The amount of Clonidine alone in Rebecca's system was enough to be fatal, the medical examiner said.
Defense attorney Darrell said his client had little to do with Rebecca's medication because he had been living apart from the family for months and returned about a week before she died.