[3] As environment commissioner, Miller issued strongly-worded reports annually, calling the province to account on its environmental commitments.

In a formal report Miller said that this, combined with cuts to staff and programs at Ministries of Natural Resources and the Environment, all "quietly and without public consultation", led to a situation with "no rules".

[7] In 2014 Miller warned that Ontario had done "very little" other than closing coal plants to meet its 2020 emissions targets, and had failed to build transit and other efficient infrastructure.

Due to his two prior candidacies, Miller's initial appointment raised the perception by the NDP and Liberal caucuses that he was a Conservative partisan.

[9] On May 19, 2015, Miller sought the Green Party of Canada nomination for the seat of Guelph in the upcoming Canadian federal election,[10] and on June 8, 2015, he was selected to run.