William Lee Amoss was born October 10, 1859, on Mt. Soma farm in Benson, Harford County, Maryland. He was educated at Oakland Academy and graduated with the equivalent of a high school degree from Eaton and Burnett Business College in Baltimore. In 1904, Amoss married Sarah Evelyn Breed, a native of Cornwall, New York. At the time of their marriage, Breed had been Superintendent of the Southern Industrial Classes of Norfolk, Virginia, a branch of the Hampton Institute, for eight years. The couple had at least one child, a daughter named Cornelia.
After serving for nine years as Secretary of the Harford County Farmers' Convention, Amoss was appointed the first director of the Department of Farmers' Institutes of the Maryland Agricultural College (MAC) in 1896. According to Amoss, his appointment came as a surprise and was accepted "only on the solicitation of friends with whom I had been associated when working for our farmers organizations for a betterment of conditions under which we were living." As director, he organized institutes in each county of the state, recruiting agricultural experts from around the country to speak to local farmers regarding the practical issues they faced every day, covering topics such as using fertilizer, raising livestock, and determining soil acidity, among many others. He reported to MAC President R.W. Silvester in 1907 that the Institutes had "shown [the farmer] that he must look to the Agricultural College and the Experiment Station for scientific information not to be obtained elsewhere." He remained director until 1910 when he was dismissed by the MAC Board of Trustees. The Board cited administrative concerns as the reason for Amoss's dismissal, indicating that the Farmers' Institutes had deviated from the Board's vision for the mission of the College. His dismissal was controversial, particularly with local farmers' organizations.
During his tenure at MAC, Amoss participated in a number of additional activities. He was one of the original founders of and subscribers to the Farmers Market Company of Baltimore City. Incorporated in 1896, it was commonly referred to as the Baltimore Market. Amoss was president of the American Association of Farmers' Institute Workers for the year 1902. In 1903 and 1904, Amoss spent a significant amount of time organizing Maryland's entry for an agricultural exhibit at the Louisiana Purchase Exposition in St. Louis, Missouri.
Amoss's name was submitted for the position of president of the Maryland Agricultural College in 1913 by George Powell, former director of the Farmers' Institutes for New York and president of the Agricultural Experts Association, though he was not ultimately considered. In 1918, Amoss was appointed Special Field Agent with the U.S. Employment Service of the Department of Labor. He dealt primarily with farm labor shortages suffered during and after World War I in New Jersey, Maryland, and Delaware. He resigned from that position in July 1919.
Amoss also maintained and developed his own farm, Mt. Soma - so named as the reverse spelling of Amos - in Benson, Harford County, Maryland. In his role as a farmer, Amoss continued to correspond regularly with state experiment stations and the U.S. Department of Agriculture. After his resignation from the U.S. Employment Service, he settled permanently into his work on Mt. Soma Farm with his family.
William Amoss died on December 11, 1933, at his residence on Mt. Soma farm. He was preceded in death by his wife.