Warner Mifflin was the son of Daniel and Mary (Warner) Mifflin. He was born on October 21, 1745, in Accomac County, Virginia, whither his grandfather, Edward, had removed from Philadelphia, Pennsylvania. He was a descendant of John Mifflin who emigrated from Wiltshire, England, sometime before 1680 and finally settled at "Fountain Green, " now a part of Fairmount Park, Philadelphia.
While General Howe was in Philadelphia and General Washington on the outskirts of the city, Mifflin was one of a committee of six appointed by the Friends' Yearly Meeting in 1777 to visit both commanders-in-chief and present printed copies of the "Testimonies" against participation in the war. They went without passports through the lines of both armies and accomplished their mission. When he was fourteen years old, on his father's plantation in Virginia, one of the younger slaves, talking with him in the fields, had convinced him of the injustice of the slave system. He soon determined never to be a slave-holder. Later, however, he came into possession of several slaves through his first wife and from his father and mother. After a period of indecision, in 1774-75, he manumitted all his slaves. Supersensitive to the promptings of conscience, he even paid them for their services after the age of twenty-one years. Thereafter, he traveled much in Quaker communities urging Friends to free their slaves. In the same cause, he appeared before various legislative bodies including, in 1782, that of Virginia, where a law was passed in May of that year removing the former prohibitions against the private manumission of slaves. In 1798, he attended the Yearly Meeting of Friends held in Philadelphia and at that time, apparently, contracted yellow fever which was then so prevalent in that city. He died of the disease soon after returning to his home in Delaware, aged about fifty-three years.
Between 1783 and 1797, Mifflin helped to draw up or to present to the Congress of the United States various petitions against slavery and the slave trade. One, dated 1789, helped to start an important debate on the powers of Congress over slavery and the slave trade under the new Constitution. In 1793 he published over his own name, A Serious Expostulation with the Members of the House of Representatives of the United States, in which he presented with no little force the anti-slavery case. In 1796, his motives and methods having been attacked by his opponents, he published in Philadelphia The Defence of Warner Mifflin against Aspersions Cast on Him on Account of his Endeavors to Promote Righteousness, Mercy and Peace, among Mankind. In this pamphlet, he sketched the activities of his life and defended his stand on such subjects as slavery, peace, and temperance.
During the American Revolution, Mifflin adhered to the Quaker peace principles and shared in the obloquy thereby entailed.
As early as 1775, Mifflin was arguing against "the pernicious use of ardent spirits. " He refused to have the least part in supporting the war, even to the use of Continental paper money. Consequently, he was dubbed a Tory, and his patriot neighbors made serious threats against him.
During most of his mature life, Mifflin lived on his farm, "Chestnut Grove, " near Camden, Delaware. He was a man of mild manner, always charitably inclined, yet of intense convictions.
On May 14, 1767, Warner married Elizabeth Johns, of Maryland, by whom he had nine children, and on October 9, 1788, Ann Emlen, of Philadelphia, by whom he had three.
