On July 20, 1850, President Millard Fillmore nominated his cabinet, having become president after Zachary Taylor died in office on July 9th. Fillmore selected Senator Daniel Webster to be Secretary of the State. Webster, a supporter of compromise legislation which included a new fugitive slave law, knew the odds of being re-elected as a Massachusetts Senator were not in his favor. Webster resigned from the Senate on July 22. He served as the Secretary of the State until his death in 1852.
Message of President Fillmore Nominating his Cabinet, 7/20/1850, McCook Collection, Records of the U.S. Senate (ARC 306305)