He was from Tipton, Staffs and was indentured as a clockmaker in 1847. He became a local preacher in the Methodist New Connexion and after preaching at the Bannisters' Great Barr Farm, he met and soon married the farmer's deeply religious daughter Eliza Bannister. Her father was so impressed by the young preacher that he paid for him to be released from his apprenticeship and set him up in business in Owen Street, Tipton, as a jeweller and clockmaker. In1865 he was listed in Jones' Mercantile Directory as a watchmaker and jeweller in High Street, Cradley Heath. His grandson, Thomas Austin Henn, opened a jeweller's in Wolverhampton and was, like his grandfather, a local preacher.
Influenced by Joseph Barker, Silas became the leader of the Barkerites in Tipton, where they erected a chapel in Waterloo Street (later sold to the Methodist Refuge Church). He left the Barkerites in 1851 and became a Wesleyan. While he was busy with his pastoral duties and preaching, his wife looked after the business, leaving Silas to deal with watch repairs in his spare time. At the age of 15 his son, John Wesley Henn, began to run their Castle Street shop in Dudley, which had been opened in 1871, so that Silas could give more time to his studies, preaching and writing. One of his earliest titles was Spurgeon's Calvinism Examined and Refuted (1858). He continued writing books and pamphlets until his death in 1902; these included The Basket of Fragments; or Broken pieces of bread for hungry souls (1871), The Beautiful in Christianity; or entire sanctification the grand-centre of the Christian Religion (1872, )The Divine Excellence of Jesus (1874?) and Truth set Free: or A Concise View of The Scripture Doctrines of Immortality and Future Punishment (1880).