According to the "Companion to Rejoice and Sing" (URC Hymnbook):

"The Melody is found in Patrick W Joyce's "Old Irish Folk Music and Songs" 1909 No 323, to the words 'With my love on the road'. The form given there corresponds with that at RS 531 (Lord of All Hopefulness) except that lines 3 and 4 each begin with a quaver.

The melody was first associated with 'Be thou my vision' in the Irish 'Church Hymnal' 1919, ......; it rapidly achieved popularity despite the difficulty congregations often found in fitting the syllables of the original irregular form of the text. 'Lord of all hopefulness', written for the tune and published in 'Songs of Praise' enlarged 1931, boosted its popularity further.

Unusually for a folk-tune, there is no melodic repitition, but typically Irish are the wide compass and the ending on the three repeated key-notes. Erik Routley's harmonization was made for 'Congregational Praise' 1951.

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The metre varies, according to the words used......"

Of the words:

"The original Gaelic hymn, of which this is a much-altered translation, dates back at least to the tenth century, and possibly earlier......"