Robert Pickton was sentenced to life in prison with no parole for at least 25 years after a sensational trial in 2007. (CBC)

The Supreme Court of Canada has broadened the scope of an appeal by convicted serial killer Robert Pickton, giving him more grounds to argue his conviction should be overturned.

As usual, the high court gave no reasons for its decision, which was released online on Thursday morning.

Pickton lost a previous appeal in June when the B.C. Court of Appeal issued a split ruling upholding his conviction, saying the mistakes made by the trial judge were not serious enough to warrant a new trial.

But because that ruling was a split decision, Pickton won the right to an automatic appeal to the Supreme Court of Canada, but only by using the arguments put forward by the dissenting B.C. Court of Appeal justice.

Following Thursday's decision, Pickton's lawyers will now be able to make arguments based on what the majority found, allowing them to argue in broader terms why the conviction should be overturned.

Pickton was sentenced to life in prison with no parole for at least 25 years after a sensational trial in 2007. The one-time pig farmer was convicted in the murders of six prostitutes, but was charged in 20 other deaths, as well.