Complex sentence: Roberts lost his seat again in the 1979 election that defeated the Trudeau government but returned yet again as a result of the 1980 election and joined Trudeau's final cabinet first as Minister of the Environment and then as Minister of Employment and Immigration.
Split into simpler sentences: Roberts lost his seat again in the 1979 election that defeated the Trudeau government. He was returned to the House yet again as a result of the 1980 election, and joined Trudeau's final cabinet, first as Minister of the Environment, and then as Minister of Employment and Immigration.