The Auditor-General's office says former National Party MP Katherine Rich has not breached any conflict of interest rules in her work for the Health Promotion Agency.
Mrs Rich says she has been vindicated by the finding, but the Green Party now wants the State Services Commission to investigate.
Mrs Rich is chief executive of the Food and Grocery Council, which represents the food industry, and was appointed by the Government to the Health Promotion Agency's board in 2011.
Last year, Nicky Hager's book Dirty Politics suggested Mrs Rich was involved in a right-wing blogger's attacks on public health researchers and academics.
Mrs Rich denied the accusations, but senior health researchers asked for an inquiry into her position with the agency.
However, in a letter to the agency released today, the Auditor-General's office said it was satisfied there were no matters it needed to investigate further.
"We have not identified problems with the management of conflicts of interest by the [agency].
"We have also looked at the process of Mrs Rich's appointment to the [agency] board. We have not identified any issues there that require comment or further investigation."
Mrs Rich declared her outside interests, which were documented and drawn to the attention of the State Services Commissioner, the letter said.
The office said it would be "too simplistic" to assume that Mrs Rich's two roles were "utterly incompatible".
It did not investigate the Dirty Politics allegations, as they did not relate to Mrs Rich's conduct on the board, it said.
Ms Rich said she was pleased with the result.
"[It] vindicates my position. Accusations that I had broken the law and not declared interests were disappointing, wrong and defamatory."
However, the Green MP Kevin Hague said he was disappointed with the finding, as there was a fundamental conflict between Mrs Rich's two roles.
The State Services Minister Paula Bennett should now ask the State Services Commission to investigate Mrs Rich's appointment, Mr Hague said.