This exquisite little poem was first published in 1837 in the 'Keepsake', an annual edited by Lady Emmeline Stuart Wortley, and was included in the edition of 1842. No alteration has been made in it since 1842.
In 1857 the title was altered from "St. Agnes" to "St. Agnes' Eve," thus bringing it near to Keats' poem, which certainly influenced Tennyson in writing it, as a comparison of the opening of the two poems will show. The saint from whom the poem takes its name was a young girl of thirteen who suffered martyrdom in the reign of Diocletian: she is a companion to Sir Galahad.
Deep on the convent-roof the snows
Are sparkling to the moon:
My breath to heaven like vapour goes:
May my soul follow soon!
The shadows of the convent-towers
Slant down the snowy sward,
Still creeping with the creeping hours
That lead me to my Lord:
Make Thou  my spirit pure and clear
As are the frosty skies,
Or this first snowdrop of the year
That in  my bosom lies.
As these white robes are soiled and dark,
To yonder shining ground;
As this pale taper's earthly spark,
To yonder argent round;
So shows my soul before the Lamb,
My spirit before Thee;
So in mine earthly house I am,
To that I hope to be.
Break up the heavens, O Lord! and far,
Thro' all yon starlight keen,
Draw me, thy bride, a glittering star,
In raiment white and clean.
He lifts me to the golden doors;
The flashes come and go;
All heaven bursts her starry floors,
And strows  her lights below,
And deepens on and up! the gates
Roll back, and far within
For me the Heavenly Bridegroom waits, 
To make me pure of sin. 
The sabbaths of Eternity,
One sabbath deep and wide--
A light upon the shining sea--
The Bridegroom  with his bride!
[Footnote 1: In 'Keepsake': not capital in Thou.]
[Footnote 2: In 'Keepsake': On.]
[Footnote 3: In 'Keepsake': Strews.]
[Footnote 4: In 'Keepsake': not capitals in Heavenly and Bridegroom.]
[Footnote 5: In 'Keepsake': To wash me pure from sin.]
[Footnote 6: In 'Keepsake': capital in Bridegroom.]