Mark Thiessen has been a photographer with National Geographic since 1990 and on staff since 1997.

He is widely published in all areas of the National Geographic Society, including National Geographic magazine, National Geographic Adventure magazine, and National Geographic Traveler magazine. National Geographic books that feature Thiessen's work include Return to Midway, which documents the discovery of the U.S.S. Yorktown, and Baseball as America, a look at the Baseball Hall of Fame.