Jewett was born on February 19, 1823, in New York City, the son of Joseph and Matilda Cornell Jewett and a descendant of Maximilian Jewett, a native of Yorkshire, England, who emigrated to America in 1638 and in 1639 was one of the founders of Rowley, Massachusetts.
Jewett's early career is obscure, but it had a westward direction. He moved to San Francisco, but later went to Colorado. His exact connection with the territory is disputed. He regarded himself as a public benefactor, but his opponents asserted that he was a holder of worthless claims and a procurer of money under false pretences. There remain only two definite records for these years: that of his marriage to Esther Garrison and his application for admission to a peace convention in 1861 as a delegate from Pike's Peak.
The Civil War years found Jewett in possession of funds and a will for peace. He was convinced that it could be obtained through European intervention. Consequently he made several visits to the continent, harried European potentates and premiers with his personal, telegraphic, and epistolary communications, and published in many pamphlets a narrative of his adventures. From time to time "Colorado Jewett" sailed to the North American continent to further his designs. Usually he preferred Canada, for there he could escape the arrest which he dreaded. Finally in January 1864 he issued from New York an appeal "to the American People and Church Universal" and began interviewing old and new acquaintances who, he hoped, were opposed to a continuance of the war. By the summer he had fallen into the hands of George N. Sanders, a foot-loose Confederate, who was voluntarily acting as a go-between for some of the Confederate commissioners who had been dispatched by Jefferson Davis to incite discontent and trouble in the Northern states. Sanders and Jewett, utilizing the latter's acquaintance with Horace Greeley, finally arranged a meeting between the editor of the New York Tribune and James P. Holcombe, one of the Confederate commissioners. John Hay was also present at the meeting, which took place at Niagara Falls on July 20. Both Greeley and Holcombe were somewhat unwillingly manipulated into this conference. At a critical time for Northern politics, it gave publicity to the pacificism of Greeley and to Lincoln's statement of peace terms in "To Whom It May Concern, " which, by insisting upon reunion and abandonment of slavery as the fundamental terms of settlement, alienated some of the president's conservative supporters. By September, however, Jewett considered peace dead.
In addition to his attempts to mediate peace during the Civil War, William also operated as a business man. There are several accounts of William acting as a mine promoter in Europe, especially England from 1860 through 1863, where he tried to sell the rights to various Colorado mines. In an effort to sell mining stakes he organized the European and Colorado Gold Mining Company in 1863. According to various accounts, he was not overly successful in promoting his various Colorado mines.
The final years of his life were spent largely in Europe. He died at Geneva in 1893.
Jewett had particular faith in "the mediation fidelity" of Napoleon III, "temporal and all powerful, " and a particular bitterness for Abraham Lincoln, "a serpent tempter" and an obstacle to peace. His activities might have been dangerous if he had not been so obviously "an irresponsible adventurer. "
In 1848 Jewett was married in St. Louis to Almira Guion, who died within a few years. He then married in 1859 Esther Garrison, who also died in a few years. Finally, Jewett married, in 1867, Charlotte Berna.
He had two daughters with his third wife: Lotta and May.
