Complex sentence: Ouimet stayed in that position under the succession of Prime Ministers who attempted to keep the Conservative government together and also served as Acting Minister of Agriculture and Acting Secretary of State for Canada under Sir Mackenzie Bowell.
Split into simpler sentences: Ouimet stayed in that position under the succession of Prime Ministers who attempted to keep the Conservative government together. He also served as Acting Minister of Agriculture and Acting Secretary of State for Canada under Sir Mackenzie Bowell.