Mark D. Sickles (born February 18, 1957) is an American politician serving as the Delegate from the 17th District of the Virginia House of Delegates. He is a member of the Democratic Party.

Sickles serves as the Chair of the Health, Welfare and Institutions Committee, Vice Chair of the Appropriations Committee and as a member in the Privileges and Elections and Rules Committee.

As an openly gay man, Sickles is the second LGBT person elected to the Virginia House of Delegates and the Virginia General Assembly (after Adam Ebbin).

Sickles is one of six openly LGBT people serving in the Virginia General Assembly (alongside Adam Ebbin, Mark Levine, Dawn Adams, Rozia Henson and Danica Roem).

In 2026, Sickles resigned from the House to join Governor Abigail Spanberger's cabinet as the Secretary of Finance, triggering a special election.

Sickles was born in Arlington, Virginia. He received a Bachelor of Science degree in Forest Management from Clemson University in 1981, a Master of Science in industrial management from Georgia Tech in 1984, and a second M.S. in Technology and Science Policy two years later.

Sickles is a fellow with the Sorensen Institute for Political Leadership at the University of Virginia.

Tragedy struck in Fairfax County in 2018 when a nine-year-old boy was killed by a motorized classroom partition. In response, Sickles drafted legislation prohibiting anyone from operating a motorized partition when students are in a room at school unless the wall has a safety sensor installed with it. He named the bill the Wesley Charles Lipicky Act in honor of the victim. The bill passed the legislature and was signed into law in May 2019.