Mark Spreitzer (born December 16, 1986) is an American politician from Beloit, Wisconsin. He is a member of the Wisconsin Senate, representing Wisconsin's 15th Senate district since January 2023. Spreitzer served four terms in the Wisconsin State Assembly, from 2015 to 2023, and before that was a member of the Beloit City Council.

Spreitzer received his bachelor's degree in political science from Beloit College.

After graduating from college, Spreitzer worked as the assistant director of alumni and parent relations and annual support at Beloit College. He also served on the Beloit City Council from 2011 to 2015, including as City Council President from 2014 to 2015.

On November 4, 2014, Spreitzer was elected to his first term in the Wisconsin State Assembly^[1] to succeed Janis Ringhand. He was reelected in 2016. A Democrat,^[2] Spreitzer served on eight committees during the 2015–16 legislative session: Jobs and the Economy, Mining and Rural Development, Natural Resources and Sporting Heritage, Public Benefit Reform, Workforce Development, Joint Committee for Review of Administrative Rules, Speaker's Taskforce on Youth Workforce Readiness, and the Legislative Council Study Committee on Rural Broadband.

Spreitzer is openly gay.^[3] He is one of three openly LGBT members of the Wisconsin State Legislature, alongside Senator Tim Carpenter and Representative Todd D. Novak.