Clayton Sidney Manness (born January 23, 1947) is a Manitoba politician. He served in the Legislative Assembly of Manitoba from 1981 to 1995. In 1983, he was an unsuccessful candidate for the leadership of the Progressive Conservative Party of Manitoba.
The son of Sidney Alfred Manness and Helen Julia Kosier, he was born in Winnipeg, Manitoba, and was educated at the University of Manitoba. He worked as a farmer before entering public life. In 1968, he married Cheryl Louise Reinsch. Manness served as President of the provincial Progressive Conservative Association in the early 1970s, and supported Sterling Lyon over Sidney Spivak in the divisive leadership challenge of 1975.
Manness was first elected to the Legislative Assembly of Manitoba in 1981, Two years later, he ran for the leadership of the Progressive Conservative party against Gary Filmon and Brian Ransom. and Government House Leader. Following a 1993 cabinet shuffle, he became Minister of Education and Training. In 2004, he campaigned for the Conservative Party of Canada.
Manness has also formed an organization called "Prairie Pulp and Paper Co." with actor Woody Harrelson, promoting the development of an environmentally friendly, non-wood-based pulp program in the province.