Joseph Johnstone Muir (July 30, 1847 – November 17, 1927) was a Baptist clergyman who served as Chaplain of the United States Senate.

Joseph Johnstone Muir was born in Parsonstown, Ireland, on July 30, 1847, to Scots-Irish parents, Alexander Johnstone and Mary Faith Stothard Muir.^[1] He worked for a time in business in Dublin before moving to the United States in 1863. He continued in business in New York.^[2]

In 1869 he was licensed to preach by the Baptist church. He served in succession: the Baptist church in Oxford, New Jersey; the East Marion Baptist Church on Long Island; First Baptist Church of Ticonderoga, New York; McDougal Street Baptist Church, New York City; the Park Baptist Church in Port Richmond, New York, on Staten Island; North Street Baptist Church, Philadelphia; the E Street or Third Baptist Church of Washington, D.C., and the Temple Baptist Church also in Washington.^[2]

He was elected Chaplain of the Senate on January 21, 1921,^[3] serving until his death in Washington on November 17, 1927.^[1][4][5] He was buried at Rock Creek Cemetery.^[6]

In 1868 he married Lizzie Glover; they were the parents of three sons and two daughters – Edward A. T. Muir, Charles Stothard Muir, John McM. Glover Muir, Florence Evelyn May Muir and Edna Alexandra Muir.^[7]