Credlin won't discount Shorten

Tony Abbott's former chief of staff Peta Credlin says the upcoming election is the government's to lose, but she didn't rule out a Labor win.

Peta Credlin.

Labor leader Bill Shorten has the potential to be a "formidable" political opponent, Peta Credlin says.

Tony Abbott's former chief of staff, who will join Sky News as a commentator during the election campaign, didn't rule out the possibility of a Labor win when questioned on Sky's PM Agenda program on Saturday night.

Ms Credlin said while she was in Mr Abbott's office Mr Shorten had started to bring unity and discipline to his team.

"I thought that in my personal interactions with him one-on-one that he had a likeability, an earthiness and a genuineness that if he was able to work that into his public presentations he'd be formidable," she said.

When asked whether her former boss had been undermined by colleagues before his ouster as PM Ms Credlin said Prime Minister Malcolm Turnbull had always made his ambitions for the top job clear, but now he had a big campaign ahead of him.

"He has my support as a Liberal," she said.