Hanmer was the son of Thomas Hanmer, eldest son of Sir Thomas Hanmer, 2nd Baronet. His mother was Arabella Charlotte, daughter of T. S. D. Bucknell. His siblings included:
* Charlotte Emma Hanmer
* Thomas Hanmer
* Margaret Maria Hanmer (wife of Richard Baker Wingfield-Baker, MP)
* Caroline Hanmer
* John Hanmer
* Sir Wyndham Edward Hanmer, 4th Bt.
* Reverend Henry Hanmer
He was educated at Eton and Christ Church, Oxford. In 1828 he succeeded his grandfather as third Baronet.
Thus said the young Alexowitz, by Danube's sweeping side,
A hundred chiefs their vassals rule, in pomp and power, and pride;
...
Clear shines the sun, but yet the cloud is grey,
And the fresh breeze comes scented with the spray
Of the wild billow, that with thundering fall,
...
'Credite me vobis folium recitare Sibyllæ.'
What, shall nought e'er be sacred, nought evade
The prying imp that pierces every shade,
...
Last night our Abbot blessed his saint
As he knelt before his tomb,
And tapers from the altar quaint,
Looked out o'er the cloister's gloom;
...
From Venice, while the moonlight falls
Brightest o'er her porphyry halls,
Gilding with unearthly ray,
Dome and column, worn and grey,
...