When Mackay resumed his duties at the Collingwood in June 1860, part of his role involved monitoring local Te Ati Awa, who were closely related to the Te Ati Awa fighting a war against the Government over a block of land in Taranaki. In 1863, just prior to the second war in Taranaki and the Government invasion of the Waikato, the Maori King sent emissaries to Collingwood to invite Maori to return to land they had been forced to leave during the Musket Wars of the 1820s. After consulting with Governor George Grey, Mackay arrested the emissaries and took them to Auckland to face sedition charges at the Supreme Court. The men were later found not guilty, but while waiting for the trial, Grey commissioned Mackay to go to the Hauraki District to mediate between local "friendly" Maori and soldiers garrisoned there. He went further to convince several "hostile" Maori chiefs to turn away from the Maori King Movement, give up their arms, and swear allegiance to the Queen. As a result of Mackay's success, Grey appointed him a Civil Commissioner of the Hauraki District, and so he moved permanently to the North Island.