The 1907 United States Senate special election in Wisconsin was held in the 48th Wisconsin Legislature between , and . The special election was necessary to complete the unexpired term of U.S. Senator John Coit Spooner, who announced his resignation in March 1907 and left office April 30. Republican former U.S. representative Isaac Stephenson was elected on the 22nd ballot after a month of voting and negotiation.
In the 1907 term, Republicans held overwhelming majorities in both chambers of the Wisconsin Legislature, so had more than enough votes to elect a Republican The main contest was in the Republican legislative caucus, where multiple progressive and conservative factions failed to reach consensus for nearly a month. Progressives ultimately coalesced around 77-year-old former U.S. representative Isaac Stephenson—who had made several previous bids for —and secured his nomination.
On April 29, by agreement between the various candidates, most legislators were allowed to be absent, with each declared candidate designating one trusted supporter to arrive and cast a placeholder vote.
On May 13, by agreement between the various candidates, most legislators were allowed to be absent, with each declared candidate designating one trusted supporter to arrive and cast a placeholder vote.
On the evening of May 16, 1907, William H. Hatton expected to secure the nomination after coming within two votes of the caucus majority earlier that day. Lieutenant Governor William D. Connor was credited with denying Hatton the nomination after he managed to convince representatives Clifford R. Goldsworthy and Elwyn F. Nelson to withhold their support. Hatton's support collapsed during the roll call vote, with Goldsworthy, Nelson, and Duncan McGregor leading the rout. Instead Isaac Stephenson achieved a majority with 55 of 98 votes cast, and the caucus then moved to make him their unanimous nominee.
The legislature re-convened in joint session on May 17. Voting proceeded exactly along party lines, with 26 members absent. Stephenson received the support of all the Republicans present and voting and was elected U.S. senator.