The younger Dayton was elected to the Trenton City Council in 1876 and served as Council President from 1876 to 1877. From 1879 to 1881 he was Trenton's City Solicitor.[3]
In 1882 Dayton was appointed Minister to the Netherlands, serving until 1885.[4] He served again as Trenton City Solicitor from 1889 to 1891. He was appointed a Judge of the New Jersey Court of Appeals in 1896 and served until his death.[5]
Dayton was a founder of Mercer Hospital, Counsel and a board of directors member for the Trenton Banking Company, a member of the Trenton Battle Monument Association, manager of the Trenton Saving Fund Society, and President of the Board of Trustees of Trenton's First Presbyterian Church.[6][7]
Dayton died in Trenton on July 28, 1897.[8] He is buried in Trenton's Riverview Cemetery.[9]
William L. Dayton Jr. was married to Harriet Maria Stockton, the daughter of Robert F. Stockton (1832–1898) and niece of John P. Stockton.[10][11][12][13]