He was an older brother of Henry Mawbey and moved to Melbourne, presumably to be with him, after getting his Certificate of Freedom in NSW in 1846.
William was born to William and Hannah Mawbey (nee Billing[s]) in Surrey, England c.1808.
In1839 (?) he was tried and convicted at Surrey Quarter Sessions for stealing a cloak.
He was sentenced to a term of seven years transportation [the average sentence] and left England on the Woodbridge on 10 October 1839.
He was 5ft 61/4in tall, Protestant and married at the time, and his occupation was that of a butcher (the same as that of his younger brother, Henry, who was already in Australia) .
He had no former convictions.[Source: State Library of Queensland, Convict Transportation Registeries Database]
On 4 May 1846 he was granted a Certificate of Freedom.[Source: NSW State Records Index to Certificates of Freedom]
The only record in the NSW Births Deaths and Marriages indexes that may pertain to him is the birth of a Mary A to William and Ann Mawby (not Mawbey) in 1847.
There is no marriage or death record for him.
As he was already married, his wife may have come to the colony to be with him, but I have not found any proof of this so far.
He probably moved to Melbourne to be with his brother.