Wendell D. Weart was born on September 24, 1932, in Brandon, Iowa. Wendell had three children from his first marriage: Brian, Kathleen, and Craig. Wendell married his second wife Leanne on August 8, 1981, and they had three children: Heather, Scott, and Randy.

Weart earned a bachelor of arts degree in geology and a bachelor of arts degree in math (1953) from Cornell College in Iowa. Weart obtained his doctor of philosophy degree in geophysics (1961) from the University of Wisconsin-Madison.