Thomas Arnold was the youngest child of William Arnold (1745-1801) and his wife Martha, the daughter of John Delafield. He was born at West Cowes on the Isle of Wight, his father serving as collector of customs and postmaster for the Isle of Wight. Arnold was first educated by his aunt Susan Delafield and then sent to Warminster School in Wiltshire. He transferred to Winchester College and in 1811 won a scholarship to Corpus Christi College at Oxford University. He then won a fellowship to Oriel College in 1815. He excelled in his studies, earning the chancellor's prize for the English essay in 1815 and the Latin essay in 1817, and made a wide variety of friends during this time of his life.

Arnold went into partnership with his brother-in-law John Buckland to operate a private school at Laleham, a village in Middlesex. Arnold and Buckland dissolved the partnership in 1824, Buckland taking charge of the younger pupils and Arnold teaching solely the older boys. In addition to serving as a headmaster, Arnold began publishing articles on Roman history to generate additional income to support his large family.

Arnold left Laleham in 1826 and became headmaster of Rugby School in 1827. He revived the school, earning loyalty from the assistant schoolmasters, and raised the educational rigor of the school. He also insisting on raising the moral tone of the school, wishing to make it a Christian school. He continued writing pamphlets and news articles.

Arnold married Mary Penrose in 1820, and they had 11 children, 9 of whom survived to adulthood. Thomas Arnold died at Rugby in 1842 and was buried in the school chapel.

[Information retrieved from Reeve, A.J.H., "Arnold, Thomas," Oxford Dictionary of National Biography.]