William was first a haberdasher (hat maker). When he migrated to New England, he became a deacon and later a lay preacher at Malden, Middlesex Co., MA and Barnstable, Plymouth Co., MA. Even though he was a lay preacher, he is commonly referred to as "Reverend William Sargent". He was admitted to the church in Charlestown, Suffolk Co., MA on 10 March 1638/9. His migration from his English established life and subsequent occupation as a lay preacher seem to indicate that William became a rather staunch Puritan.

He appeared to first follow in his father's political footsteps and was elected Senior Bailiff of Northampton in 1632-3.

William first made Freeman in England at Northampton on 20 July 1626, at which time he is called the "son of Roger Sargent". In America, William took the Oath of Freeman on 2 May 1639 in Charlestown, Suffolk Co., MA and made freeman in Plymouth Colony in 1657.

Like his father, he lived in All Saints parish, Northamptonshire, England. His name appears for the last time in the parish register of All Saints on 22 January 1636/7 at the baptism of his daughter Mary. Although the details of his migration are currently lost, he had settled in Charlestown, Suffolk Co., MA by 1638/9.

Circa 1627 when William was 25, he first married Hannah [surname not known], in All Saints, Northampton, Northamptonshire, England. Hannah died in 1632 and was buried on 25 September 1632 in All Saints, Northampton, Northamptonshire, England. They had 4 daughters.

Circa 1634 when William was 32, he second married Mary/Marie [surname not known], in All Saints, Northampton, Northamptonshire, England. She died circa 1637 in Northampton, Northamptonshire, England. They had two daughters, Mary and Sarah.

Sometime before 17 March 1638/9, when "Rev. William Serjeant" was 36, he third married Sarah [surname not known], in Charlestown, Suffolk Co., MA. She was admitted to the church at Charlestown on 17 March 1638/9. They had two sons, John and Samuel, and one daughter, Ruth.

William's will was written on 9 March 1679/80 and is also reprinted in Aaron Sargent's book, Sargent Genealogy of 1895. The will was proven on 3 March 1682/3 and devised to his wife and six children.