He was a grandson of Jesse Ladd and Ruby Brewster, who were among the original pioneers in Madison, Lake County, Ohio. Ruby was a granddaughter of Oliver Brewster and Martha Wadsworth Brewster, a poet and writer, and one of the earliest American female literary figures.
He was a descendant of Elder William Brewster (c. 1567 – April 10, 1644), the Pilgrim leader and spiritual elder of the Plymouth Colony and a passenger on the Mayflower, and Governor William Bradford (1590–1657) of the Plymouth Colony and a passenger on the Mayflower. He was also a seventh generation direct lineal descendant of Daniel Ladd, Sr. (1613–1693).
He early gave indications of the studious habits that characterized him through life. When he was eight years old his first savings, two dollars, were spent for a copy of Josephus and Plutarch, while when eighteen years of age he read Kant's Critique of Pure Reason.
Most of his work in preparing for college was done by himself, only a portion of the time being given to the curriculum in the Painesville High School and at the college preparatory school of the Rev. Mr. Brayton in Painesville, Ohio.
After graduation, he went into business with his father. His constant studies, however, seemed to turn his steps naturally toward a higher institution of learning, with the result that in 1866 he went to the Andover Theological Seminary.
During 1879 to 1882 he lectured on theology at Andover Theological Seminary, and in 1883 at Harvard University, where from 1895 to 1896 he conducted a graduate seminar in ethics.
Between 1892 and 1899, at the invitation of the government of Japan, he served as a diplomatic adviser and helped the cabinet under Prime Minister Hirobumi Ito (1841–1909) to promote mutual understanding between Japan and the United States.
He was much influenced by the German philosopher Hermann Lotze, whose Outlines of Philosophy he translated (6 vols., 1877) and was one of the first to introduce (1879) the study of experimental psychology into America; the Yale psychological laboratory being founded by him. In 1887, he published Elements of Physiological Psychology, the first American textbook to include a substantial amount of information on the new experimental form of the discipline.
Elizabeth Tudor Ladd, (1882–1965), married Walter Aldrich Barrett.
He married second, on December 9, 1895, Frances Virginia Stevens, born February 9, 1866, at New York City, the daughter of Dr. George T. Stevens and Harriet Weeks Wadhams. There were no children from the second marriage.
^Daniel Ladd, Sr. was born in 1613 in Deal, Kent County, England. He died on July 27, 1693 at the age of 80 in Haverhill, Essex County, Massachusetts. On March 24, 1633, took the "Oath of Supremacy and Allegiance, thus enabling him to leave London, England and take the Vessel "Mary And John" (Robert Sayres, Master). First mentioned in Ipswich town records in February 1637; in Salibury, MA, October 29, 1639, and was one of the first settlers of Haverhill, MA. On February 5, 1637 he was granted six acres of land on which he built a house ... On October 29, 1639 and September 7, 1640, he had land granted to him in Salisbury. From Salisbury he removed to Haverhill where he died. His house in Haverhill was in the village, his planting lots were in two different locations while his meadows were located in seven different locations. In 1659 Daniel erected a sawmill with Theophilus Shatwell on the Spiggot (Spicket) River. It was built within the present limits of Salem, New Hampshire and was the first mill erected on that stream. An extensive account of Daniel Ladd is provided on pages1 through 11 of "The Ladd Family" as well as on pages 12-21 of "Lest We Forget: AFamily Saga" From the NEHG Register, Vol 38, p. 345. According to the record of the Quarterly Court of Essex County: "Daniel Ladd was accounted a man of good social graces." He held at one time the rank of lieutenant.[clarification needed]