Whilst Dean, he was a founding member of the Hampshire Horticultural Society in 1818 (Dean Garnier's Garden in Winchester's cathedral close is named after him) and, in the 1860s, an 'anti-muckabite' campaigner for a sewerage system for Winchester (with the road to the town's first sewerage pumping station later being named after him).
His son, also called Thomas Garnier, rowed in the first university boat race, was Dean of Lincoln from 1860-1863 and married Lady Caroline Elizabeth Keppel, daughter of William Charles Keppel, fourth Earl of Albemarle, and his wife Elizabeth Southwell, daughter of Edward Southwell, 20th Baron de Clifford. Another son was Keppel Garnier, Commander in the Royal Navy.
- Simmonds, Joan. "A Brief History of Bishopstoke". Bishopstoke Parish Council. Retrieved 2007-01-07.[dead link]