Lemke was the attorney general of North Dakota from 1921 to 1922. He later was elected to the United States House of Representatives in 1932 on the Republican Party ticket. He served four two-year terms in Congress.

While in Congress, Lemke earned a reputation as a progressive populist and supporter of the New Deal, championing the causes of family farmers and co-sponsoring legislation to protect farmers against foreclosures during the Great Depression.

In 1936, Lemke co-sponsored the Fraizer-Lemke Bill, which would have provided for government refinancing of farm mortgages. President Franklin D. Roosevelt refused to support Lemke on that issue and ultimately sank the bill.

Later in 1936, Lemke accepted the nomination of the Union Party, a short-lived third party, as their candidate for President of the United States. He received 892,267 votes, or just under 2ationwide, and no electoral votes (see also: U.S. presidential election, 1936). Simultaneously, he was reelected to the House of Representatives as a Republican. Many believe Lemke's acceptance of the Union Party nomination in 1936 was out of bitterness toward Roosevelt over the farm mortgage issue.

In 1940, after having already received the Republican nomination for a fifth House term, he withdrew from that race to launch an unsuccessful run as an independent for the U.S. Senate. He ran again for Congress in 1942 as a Republican and served four more terms, until his death in 1950.

Lemke died in Fargo, North Dakota and is buried in Riverside Cemetery.