Before discovering CrossFit, Starrett paddled for the US canoeing and kayaking teams. As a paddler, he won two national championships and competed in two world championships before receiving a repetitive strain injury. In 2004, he and his wife Juliet began CrossFit training, eventually opening one of the first CrossFit gyms in 2005.

Starrett received a Doctor of Physical Therapy from Samuel Merritt University in 2007. In 2009, the Starretts started their fitness website MobilityWOD, which has been praised as a top fitness blog by Outside Magazine and other outlets.

Starrett is the author of three books on fitness and mobility. Before writing full-length books, Starrett contributed articles to the Crossfit Journal, focusing on the basics of posture and gait. He has continued in this vein with his first book, The Supple Leopard (2013), which highlights basic mechanics and range of motion. The Supple Leopard was generally well received, making the New York Times bestselling Sports books list, though it did receive criticism for being "a trial and error method rather than a system of standard operating procedures to diagnose and fix movement."

Following the success of Supple Leopard, Starrett released Ready to Run with coauthor T.J. Murphy in 2014. Ready to Run examines shoe choice and foot health as well as exercises to improve running biomechanics and mobility. Erin Bresini, writing for Outside Magazine described the book as offering relief from running injuries. In his review for Breaking Muscle, Doug Dupont found the book "simple and accurate," but noted that the book "might not meet expectations" since it does not contain actual training plans.

Starrett's 2016 book Deskbound was coauthored with his wife Juliet Starrett and Glen Cardoza. Deskbound describes the physiological and epidemiological effects of a sedentary lifestyle. The book was precipitated by the launch of the Starretts' nonprofit, Stand Up, which raises money to purchase standing desks for children in schools.