J. Nicholas Mandziuk was born in the village of Kryvche, Borshchiv county, Crownland of Galicia, Austro-Hungarian Empire (now Ukraine) on December 13, 1902. In 1904, he immigrated with his parents to Canada, where they settled in the Ashville district of Manitoba. He graduated from the Teacher's College in 1921 and taught for several years in various schools in Manitoba and Saskatchewan. In 1933, he graduated with honours from the University of Manitoba with a Bachelor of Law degree. He practiced law in Oakburn, Manitoba and, in 1961, was honoured by being named Queen's Council. In Oakburn, he was active in community affairs, serving as Chairman of the Oakburn School District, President of the Oakburn Board of Trade, and Manager and founding member of Oakburn Credit Union. He was also active in the Ukrainian community, where he served on the following boards and associations: member and Chair of the Board of Oakburn National Home, founding member and executive member of St. George's Ukrainian Orthodox Church in Oakburn, President of the Manitoba Ukrainian Self-Reliance Association, and General Secretary of the Ukrainian Canadian Congress. His active role in the Ukrainian community resulted in his being awarded the Shevchenko Medal by the Ukrainian Canadian Congress and the Canada Service of Excellence Award by the Ukrainian Self Reliance League (USRL).

In 1957, Mandziuk ran as the Progressive Conservative candidate for the Manitoba federal riding of Marquette. He successfully won the riding and was re-elected in four subsequent elections. As a Member of Parliament, he served on various committees and represented Canada at international conferences, including acting as Chairman of the Manitoba Caucus, Member of the External Affairs Department, and Chairman of the Private Bills Committee, and serving on Canadian delegations to the United Nations, to the NATO Parliamentary Conference, to the Inter-Parliamentary Conference and to the Inter-Parliamentary Union.

Nicholas Mandziuk died on September 7, 1969. He was survived by his wife Mary (nee Wlasiuk), their daughters, Sonja Bejzyk and Darcia Zemlianski, and two grandchildren.