O'Connor ran as the New Democratic Party candidate in the 1990 provincial election in the riding of Durham—York. He wasn't nominated until two weeks after the start of the election. During the campaign he said the major issues were lack of approvals for expanding schools and rising property taxes. He defeated Liberal incumbent Bill Ballinger by 1,230 votes. After the election he promised to clean up pollution in Lake Simcoe and Musselman Lake. He was appointed as Parliamentary assistant to the Minister of the Environment, Ruth Grier.