Maine Governor Angus King nominated Robert Spear as commissioner of the Maine Department of Agriculture on March 12, 1999. He is the first dairy farmer named agriculture commissioner in Maine in more than three decades. "[Spear's appointment] is a crucial part of our strategy to reinvigorate Maine's agriculture industry," King said after naming Spear to the position. "We were looking for someone with a knowledge of agriculture, the political process and who could work as a key administrator."

Spear served in the Maine House of Representatives from 1990 to 1998, serving as chairman of the agriculture and taxation committees. He is president of Spear Farms, Inc., a family dairy and vegetable farm and is active in his local Soil and Water Conservation District.. In 1990, he received the "Conservation Farm of the Year Award" from the National Association of Conservation Districts (NACD).