He was born on 13 November 1803 at Fetteresso near Stonehaven, Kincardineshire, the son of John Longmuir, a sailor, and his wife, Christian Paterson.
John Longmuir was Keeper of the Ruins of Dunnottar Castle and at one time butler at Ury House, Stonehaven.
In 1824 he was teaching in Aberdeen, living at 62 Loch Street;[2] he taught for some years in schools at both Stonehaven and Forres.
This was renamed Commerce Street Free Church in 1881 when Longmuir retired and was replaced by Rev A. Murray Scott.
[4] Longmuir was for some years lecturer on geology at King's College, Aberdeen, and in 1859 was granted the honorary doctorate of LL.D.
His edition of Alexander Ross of Lochlee's Helenore (Edinburgh, 1866) appeared with a life of the author.
A revision of John Jamieson's etymological Scottish Dictionary provided his major work.
[3] Several of Longmuir's sermons were published separately, generally with an original hymn attached.