The decision former Queensland premier Campbell Newman regrets “more than any other” in his 13-year political career was his appointment of controversial chief justice Tim Carmody to the supreme court.

The revelation comes in the authorised biography Can Do: Campbell Newman and the Challenge of Reform, due for release in October.

The book, by journalist and former parliamentarian Gavin King, says Newman’s treasurer, Tim Nicholls, and chief of staff, Ben Myers, both advised Newman against Carmody’s elevation.

Carmody was awarded the position by Newman in June 2014. He had not previously sat on the supreme court and had served only nine months as a chief magistrate. Long-serving judges were overlooked for the position.

His appointment drew criticism from the legal profession. The head of Queensland’s court of appeal, Margaret McMurdo, later refused to work with him in any court.

Others criticised the decision as being a “captain’s pick”, since Carmody was close to Newman and the LNP government. It became one of the most contentious appointments in modern legal history, and Carmody ultimately stood down barely 12 months into the job.

Newman was ejected from office after just one term, and the Carmody appointment was seen as contributing to the government’s demise.

But while Newman says the decision to appoint Carmody was a bad one politically, he told the Sunday Mail in an exclusive interview published on Sunday that he still believed Carmody was “the right guy’’ for the job.

“It was about reform,” Newman said. “The courts and the legal system need to be reformed.”

During his time as chief justice, Carmody angered his legal peers by directing magistrates not to interfere with the LNP’s strict anti-bikie laws, and also issued an extraordinary directive to ensure he, rather than individual judges, would preside over disputed bail applications for accused bikies.

Newman also told the Sunday Mail that the boost the federal Coalition government had seen in the polls since replacing Tony Abbott as prime minister with Malcolm Turnbull proved that the LNP, too, could have won the 2015 state election if he had been allowed to stand aside.

Newman twice offered his resignation after the LNP suffered a devastating defeat in the Stafford byelection, triggered when the LNP’s Chris Davis quit parliament claiming the Newman government would not listen to dissenting views.

Newman said had he also stood aside following the defeat, “the LNP could have won the election in my view”.

Labor’s Annastacia Palaszczuk took power following the election in January, deposing the Newman government in one of the greatest electoral landslides in Australian political history.

Newman said he took responsibility for the defeat, and the huge swing against the LNP.

“There were mistakes that were made,” he said.

“Even if they were made by other people, I take responsibility for them because at the end of the day the buck stops with the leader.

“We were upfront with people and in your face. We didn’t do things that were against people’s interests. We did hard things but they had to be done and they still have to be done. We clearly, politically got many things wrong and that’s my fault.’’

Newman said going to an early election was the right move, giving growing dissent against the federal Abbott government which would have only made campaigning harder.

“That’s why the election was on January 31, because I could smell trouble coming and I wanted it [the election] as soon as possible,” he said.