Born in St. Louis, Missouri, Fleissig earned a Bachelor of Arts degree in 1976 from Carleton College and a Juris Doctor in 1980 from Washington University School of Law.

[1] During her third year of law school, she worked as a law clerk for Judge Edward Louis Filippine, a judge on the United States District Court for the Eastern District of Missouri.

[1][3] In February 2009, Fleissig submitted her resume for a federal district court vacancy in St. Louis to United States Senator Claire McCaskill.

After interviews with representatives of the United States Department of Justice and the White House, Fleissig was nominated on January 20, 2010 to the position by President Obama, to replace Judge E. Richard Webber, who assumed senior status on June 30, 2009.

[3] As of Oct. 1, 2018, she is Chair of the Committee on Court Administration and Case Management (CACM) of the Judicial Conference of the United States, and has continued in that role through at least June 2019.