His most important contribution to the science of hanging was his refinement of the long drop method developed by William Marwood, whom Berry knew quite well.
His improvements were intended to diminish mental and physical suffering and some of them remained standard practice until the abolition of capital punishment for murder.
Since he did not earn enough for the upkeep of his family, he applied for the post of executioner after William Marwood died in 1883 but was unsuccessful despite being shortlisted, until the short period of Bartholomew Binns in office was over.
He executed an old Birmingham man named Moses Shrimpton who had already been arrested for poaching in February 1848, and as he was stealing game many years later, he murdered Constable Davies, a policeman that tried to stop him.
He executed Rudge, Martin, and Baker, a gang of three that committed a jewel robbery which resulted in the death of Constable Byrnes and the wounding of two other policemen.
In his book My Experiences as an Executioner James Berry makes no mention of the Whitechapel murders for which there have always been multiple suspects.
Smith Wigglesworth, the evangelist and preacher, records his conversion to Christianity, in a sermon which was later published in Faith that Prevails (1938): In England they have what is known as the public hangman who has to perform all the executions.
At the end of two and a half hours he was graciously saved.Following his conversion to Christianity, James Berry became a prominent campaigner for the abolition of the death penalty.
Berry died at Walnut Tree Farm, 36 Bolton Lane, Bradford, West Yorkshire, on 21 October 1913.