He served as the longtime Progressive Conservative Member of Parliament for Yukon, and was Leader of the Opposition and the third deputy prime minister of Canada.

His mother, Mabel Elizabeth (née Davies), was an immigrant from Wales, and his father, Ingvard Eversen Nielsen, was a Danish-born constable in the Royal Canadian Mounted Police.

He was a backbench MP during the Diefenbaker government but became prominent during the Conservative Party's long period in Opposition during the 1960s and 1970s joining the shadow cabinet in 1964.

In 1978, he ran for the leadership of the newly formed Yukon Progressive Conservative Party as it prepared for the territory's first partisan elections but was defeated by Hilda Watson by one vote.

After the Tories were defeated in the 1980 election, he served as Opposition House Leader from 1981 until 1983, and engineered the "Bell Ringing Affair" to protest the Liberal government's omnibus energy bill.

The business of the House of Commons of Canada ground to a halt for three weeks because the Opposition refused to respond to the bell summoning Members of Parliament to come to the chamber to vote.

His habit of stonewalling questions had the effect of prolonging the shelf life of political scandals in Parliament, and thus hurt the government's reputation.