He later returned to Kansas State, earning a Ph.D. in economics with a specialization in agricultural policy and international trade in 1987.
Lambert served for more than 15 years in various positions with the National Cattlemen's Beef Association, including chief economist for that organization.
In the U.S. Department of Agriculture, Lambert helped to oversee policy development and the day-to-day operations of the 3 agencies that comprise the Marketing and Regulatory Programs mission area: the Animal and Plant Health Inspection Service, the Agricultural Marketing Service, and the Grain Inspection, Packers, and Stockyards Administration.
[1] When bovine spongiform encephalopathy was detected in December 2003, Lambert became a primary member of the team of USDA and Administration officials assembled to help reopen international markets to U.S.
In March 2004, Lambert led the U.S. delegation that participated in the first meeting of the parties to the Protocol on Biosafety, held in Kuala Lumpur.