William Kneass was born on September 25, 1780 in Lancaster, Pennsylvania, United States. A grandson of Johan Christian Kneass, probably a native of the Palatinate, who arrived in Philadelphia in 1753, William was the son of Christopher and Anna Justina (Feltman) Kneass.
Kneass received his education in Philadelphia and where he learned the art of engraving.
In 1804 Kneass set up in business for himself. He not only engraved in line, which was his specialty, but was proficient in stipple engraving, and also made use of aquatint. In the exhibition of the Pennsylvania Academy of the Fine Arts in 1813, he showed an aquatint engraving of "A View of Quebec, " after a sketch by William Strickland. This plate appeared in the Port Folio for April of that year.
Kneass engraved plates for the Analectic Magazine, usually in line, and for the American edition of Abraham Rees's Cyclopaedia (1820 - 1824). These engravings were principally in the department of mechanics. Several portraits in stipple by Kneass are listed in Stauffer's American Engravers, among them those of Joseph Black, Benjamin Lay, and William Penn. He also engraved vignettes for title pages and for commercial purposes.
In 1817 Kneass formed a partnership with James H. Young, another line engraver, under the style of Kneass, Young & Company, which continued until 1820. Later he formed a partnership with George Delleker. On January 29, 1824, he was appointed engraver and die-sinker to the United States Mint, and held that office until his death.
For the gold coinage in 1834 and 1838 and for the silver coinage in 1836, 1837, and 1838, he engraved many of the dies. His name appears on a pattern half-dollar of 1838, but the silver dollar of 1836 and another pattern half-dollar of 1838 were the work of his assistant, Christian Gobrecht. During the War of 1812, Kneass was a volunteer associate of the Field Engineers who constructed fortifications on the western front of Philadelphia. In 1815 he engraved a plan of this work, after a drawing by Strickland.
He took a general interest in science andin 1815 in a rather jocular and irregular manner, he suggested to Samuel Vaughan Merrick the founding of the Franklin Institute. Young Merrick took him seriously, and, after an earnest conference with Kneass, called the meeting which led to the Institute's formation.
A portrait of Kneass, by Sully, was exhibited in 1841 by the Artists' Fund Society, Philadelphia.
Kneass's most ambitious plate probably was the line-engraving of Masonic Hall, Philadelphia, after a drawing by William Strickland. This was of large folio size. He also made some major contributions to US coinage and the Mint. He was credited with designing of Capped Bust Half Dime and Capped Bust Silver Dime.
Kneass was one of the earliest members of the Academy of Natural Sciences, joining in 1814. He was also a member of the Beef Steak Club of Philadelphia, an organization of artists, wits and literary characters of that city who frequented his studio,
Kneass was twice married: first on June 23, 1804, to Mary Turner Honeyman, by whom he had six children, among them Samuel Honeyman Kneass, engineer and architect, and Strickland Kneass, engineer. His first wife died in 1826, and subsequently he was married to Jane Kramer, who left no issue.
