 Born in Upper Canada, near Detroit, Isaac Messmore grew up in Michigan and later studied law as a young man, graduating from the Richmond Law School in Virginia; he went on to live in La Crosse, Wisconsin, where he practiced law in the 1850s.In 1861, he served in the Wisconsin State Assembly as a Republican.Later in 1861, he was appointed a Wisconsin Circuit Court judge; however, his appointment to the bench was ruled to have been improperly authorized by the governor, and thus invalid.