Jay Handel, a former fish farm worker was convicted in Campbell River by a jury that deliberated for two days, the Canadian Broadcasting Corp. said.
Provincial Supreme Court Justice Jim Taylor gave Handel an ominous reprimand after the verdicts were read.
"Without good reason, you took the lives of six young defenseless people and you will live with that for the rest of your life," the judge said.
Handel had pleaded not guilty on grounds he was mentally ill at the time his children, ranging in age from 2 to 11, were drugged, strangled and shot.
Prosecutors said Handel killed the children on March 11, 2002, to punish his wife Sonya, who was planning to leave him.
He received an automatic life sentence with no chance of parole for 25 years.