The newspaper reported being told by an undisclosed source the 6-foot-8 Ariza, 24, signed a five-year, $33 million deal late Thursday.
The 6-foot-7 inch Artest, 29, had told ESPN Thursday he has reached a verbal agreement with the Lakers and will play for the mid-level exception, roughly $18 million for three years.
Artest added the Lakers jumped at the chance to give him a multiyear deal when Houston offered him only a one-year contract.
"The Lakers really made me feel wanted," Artest told the Chronicle. "I look forward to helping the Lakers defend their championship."
Ariza was the sixth man while helping the Lakers beat Orlando in five games on the way to their 15th NBA title on June 15.
He scored 11.3 points in 23 post-season contests.