Loewen entered political life in Manitoba's 1999 provincial election, winning election for the newly created south Winnipeg constituency of Fort Whyte. Running as a Progressive Conservative, he defeated New Democrat Bidhu Jha by 3,665 votes. The New Democratic Party won the election, and Loewen became a Member of the Legislative Assembly (MLA) in the Official Opposition. He was appointed as his party's critic for Intergovernmental Affairs, and was later promoted to Finance Critic. Considered a rising star in his party, there was some speculation that he would run to succeed Gary Filmon as party leader in 2000. He decided against this when the party establishment united behind Stuart Murray.