He assisted his father on his farm at Mangapai and was a reporter on the Auckland Weekly News.

In 1864 he went to the West Coast goldfields of the South Island, working as a miner at the Greenstone, Red Jack's Gully, and other districts of the Grey.

On the opening of the Thames as a goldfield, McCullough returned to Auckland, and 'tried his luck' on the new field, acting as a miner and mine manager for several years, and subsequently joining the Times as mining reporter.

As a Freemason, McCullough held the office of right worthy provincial grand master of the North Island, Scotch Constitution, he succeeded Frederick Whitaker in this position.

[2] McCullough was called to the Legislative Council by the Ballance Ministry on 15 October 1892 as the representative of a goldfields district.