Answer
John Diefenbaker was defeated by Lester B. Pearson in the 1963 Canadian federal election, and as a result, Pearson became the Prime Minister of Canada. Diefenbaker had been Prime Minister since 1957, but his popularity had declined in the years leading up to the 1963 election. Pearson's Liberal Party won a majority government in the election, and Diefenbaker's Conservative Party was reduced to a minority.