The Inner Temple database of admissions has him admitted, from St Catherine’s, Oxford, on 23 Apr 1847, called to the bar on 7th May 1847 and died on 10th Aug 1878.  The database also notes that he was admitted to Lincoln’s Inn on 26th Jan 1844.  He was said to be the only son of his father, Rev Littleton Powys, clergyman of Fitch Marsh, Northants:

Powys, Littleton

Type of entity                          Individual person
Parallel forms of name                  Powis, Littleton
Primary address: street                 St Catherine Hall
Primary address: town                   Cambridge
Primary address: county                 Cambridgeshire
Primary address: country                England
Secondary address: street               Lincoln's Inn
Secondary address: town                 Holborn
Secondary address: county               London
Secondary address: country              England
Father                                  Powys, Littleton, Hon Rev
Father's occupation                     clergyman
Father's address: town                  Fitch Marsh
Father's address: county                Northamptonshire
Father's address: country               England
Relationship                            only son
Deceased                                Yes
Functions, occupations and activities   MA
Admission year                          1847
Admission date                          23-04-1847
Call year                               1847
Call date                               07-05-1847
Date of death                           10-08-1878
Name change                             to Hatsell.
Notes                                   Admitted to Lincoln's Inn 26-Jan-1844.
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Thanks to Di Cummings, I have the text of the Royal Licence for his name change (from the London Gazette):

Whitehall, March 11 1838

The Queen has been please to grant unto Littleton Powys, of Cavendish-crescent, in the city of Bath, in the county of Somerset, Esquire, and of the Inner Temple, London, Barrister-at-Law, Honorary Master of Arts of the University of Cambridge, only son and heir of the Reverend Littleton Powys (commonly called the Honourable and Reverend Littleton Powys), Rector of Titchmarsh, in the county of Northampton, deceased, by Penelope, his wife, eldest daughter of James Hatsell, of Spring-garden-terrace, in the parish of St Martin-in-the-Fields, in the county of Middlesex, and sister of Henry Hatsell, later of Shillingthorpe, in the county of Lincoln, Esquires, both deceased, Her royal licecne and authority that he may take and henceforth use the surname of Hatsell, in addition to and before that of Powys:
And also to command that the said royal concession and declaration be recorded in Her Majesty’s College of Arms , otherwise to be void and of none effect.

My guess is that Henry Hatsell, his uncle, put a name and arms clause in his will.  But I can find no record of Henry’s death nor of his will.
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Di Cummings also documented his stay in Australia between 1836 and 1838, giving documentary evidence for
1. His outward journey on the ship Cygnet,
2. His purchase, in hit father’s name, of an acre of land in Grote Street, Adelaide,
3. His attendance at the proclamation of Victoria as Queen in 1837,
4. His journey to Sydney and then return to Liverpool in 1838.
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