Born in Twickenham, Middlesex, in England, he became interested in Scottish Gaelic after being stationed in Scotland with the army and working with the Ordnance Survey.

He illustrated, printed, bound and marketed his dictionary with help from his children and wife Mary McDougall (from Kilmadock) whom he had married in 1896,[1] herself a native Gaelic speaker, teaching himself the skills required.

[2] The fame of his dictionary grew far more after his death, although he was recognised during his lifetime, having been made an honorary life member of both the Gaelic Society of London and An Comunn Gàidhealach.

Dwelly's illustrated Scottish Gaelic dictionary, consisting of well over one thousand pages, was truly a marvellous achievement in its day, particularly in view of the difficult circumstances which he faced in preparing it.

Scottish Gaelic speakers were generally not taught to read and write in their native language and were therefore unable to provide correct spelling, which created enormous difficulties in preparing the dictionary.

Due to a change in copyright law and various other complications, it eventually took a German learner of Scottish Gaelic, Michael Bauer, over 10 years to complete the digitisation.