He began his criminal career as a counterfeiter, but eventually turned to highway robbery.
Known as the "Robin Hood of Pennsylvania", there are numerous stories of Lewis having "robbed from the rich to give to the poor".
Many of these tales are more folklore than history, though there are several newspaper accounts from the period that describe Lewis as assisting the downtrodden, taking pity on some intended victims, and befriending many locals, who often assisted him in evading justice.
Lewis and his gang frequently used a network of caves throughout central Pennsylvania as hideouts and stores for stolen goods, Indian Caverns claimed to be one such hideout during its time as a show cave.
On his deathbed in Bellefonte Jail, he wrote an autobiography in the form of confessions which was published at the time, excerpts of which have appeared in several newspaper accounts since.