He was born at Stockwell, London, the son of John Letts, a bookbinder and printer of the Royal Exchange.
Additionally, his factories at North Road, New Cross printed interest tables, specialist clerical and medical diaries, calendars, parliamentary registers, ledgers, and logbooks.
Letts' publications became ubiquitous, being used by many of the well-known Victorian writers and diarists who were well acquainted with the product range.
For example, writing in the Cornhill Magazine, William Makepeace Thackeray noted he preferred a Letts No.
Thomas was joined in the family business by his son, Charles, and together they raised capital for expansion into a limited company in 1870, trading as 'Letts, Son & Co.' However Thomas died soon afterwards, being buried in West Norwood Cemetery in a Grade II listed monument.