Born in Peterhead, Aberdeenshire, Scotland, to a Presbyterian family, he received an M.A. from the University of Aberdeen. Keith joined the Religious Society of Friends in the 1660s, accompanying George Fox, William Penn, and Robert Barclay on a mission to the Netherlands and Germany in 1677. In 1685, three years after Barclay had been made the nonresident governor of the Province of East Jersey, Keith traveled there to take the post of Surveyor-General. In 1686 he ran the first survey to mark out the border between West Jersey and East Jersey, which is today still known as the Keith line. He moved to Philadelphia in 1688 to serve as headmaster at the Friends School there. For his survey work, the Proprietors gave him large grants of land including seven hundred acres in Monmouth County where he founded the town of Freehold. He established his home in a Quaker settlement near Topanemus where he helped to build a meeting house in which he preached to the people on the Quaker faith. Around 1691 Keith decided that Quakers had strayed too far from orthodox Christianity and began to have sharp disagreements with his fellow believers. He first broke with Philadelphia Yearly Meeting to form a short-lived group called the Christian Quakers in the colonies. In 1693, he and his fellow Keithians published An Exhortation & Caution to Friends Concerning Buying or Keeping of Negroes, one of the earliest printed antislavery tracts in British North America. David Brion Davis, a leading scholar of abolition and slavery, argues that Keith's Exhortation foreshadowed "the major religious themes of nineteenth-century abolitionism." After returning to England, he was disowned by London Yearly Meeting in 1694. In 1699 he attacked William Penn and other Quakers as "Deists". He was ordained to the Church of England ministry in May 1700. Sponsored by the Society for the Propagation of the Gospel in Foreign Parts, Keith returned to the American colonies as a missionary from 1702 to 1704, trying to win over Quakers and others. Keith invigorated Anglican congregations in Perth Amboy, Burlington and Concord Township, Pennsylvania. He preached in Williamsburg, Virginia in 1703, and left behind his daughter, Anne, who had likewise returned to the Anglican fold, unlike her husband, Quaker George Walker of Old Point Comfort. Upon returning to England, Keith served as rector at the parish of Edburton, Sussex until his death on 27 March 1716. He is buried in the churchyard and his grave has an inscribed stone installed in 1932.
