He said the jury had made clear findings and there was no assurance Craig would not appeal if a new trial also went against him.
"So an appeal now could get to the key issues directly. It is the best way forward."
Craig said Williams had every right to appeal, but he believed a retrial was the right way forward.
He said Justice Katz's decision said a miscarriage of justice had occurred so he was not willing to accept the jury's decision he had defamed Williams.
"Her Honour said it was a miscarriage of justice so I'm not going to agree to a result based on a miscarriage of justice."
He said Katz had recognised Craig was under attack from Williams at the time and had a right to respond.
The defamation trial unfolded after Craig's press secretary, Rachel MacGregor, resigned suddenly just 48 hours before the 2014 general election.
The resignation was high profile and there was much speculation about why she left.
Weeks later MacGregor turned to Williams for support, and told him she had made a complaint to the Human Rights Commission alleging that Craig had sexually harassed her.
She shared letters and poems the politician had sent her. Williams then revealed the details to other Conservative Party members.
When Craig found out, he publicly claimed Williams was part of a group of "culprits" determined to have him removed as party leader through a "campaign" of "false accusations".
Williams then filed defamation proceedings in the High Court, saying he did not lie about Craig.