By this time Jonson had begun to write original plays for the Admiral's Men; in 1598 he was mentioned by Francis Meres in his Palladis Tamia as one of "the best for tragedy." None of his early tragedies survive, however. An undated comedy, The Case is Altered, may be his earliest surviving play.
In 1598 Jonson produced his first great success, Every Man in His Humour, capitalising on the vogue for humorous plays which George Chapman had begun with An Humorous Day's Mirth. William Shakespeare was among the first actors to be cast. Jonson followed this in 1599 with Every Man out of His Humour, a pedantic attempt to imitate Aristophanes. It is not known whether this was a success on stage, but when published it proved popular and went through several editions.
Notwithstanding this emphatically Protestant grounding, Jonson maintained an interest in Catholic doctrine throughout his adult life and, at a particularly perilous time while a religious war with Spain was widely expected and persecution of Catholics was intensifying, he converted to the faith. This took place in October 1598, while Jonson was on remand in Newgate Gaol charged with manslaughter. Jonson's biographer Ian Donaldson is among those who suggest that the conversion was instigated by Father Thomas Wright, a Jesuit priest who had resigned from the order over his acceptance of Queen Elizabeth's right to rule in England. Wright, although placed under house arrest on the orders of Lord Burghley, was permitted to minister to the inmates of London prisons. It may have been that Jonson, fearing that his trial would go against him, was seeking the unequivocal absolution that Catholicism could offer if he were sentenced to death. Alternatively, he could have been looking to personal advantage from accepting conversion since Father Wright's protector, the Earl of Essex, was among those who might hope to rise to influence after the succession of a new monarch. Jonson's conversion came at a weighty time in affairs of state; the royal succession, from the childless Elizabeth, had not been settled and Essex's Catholic allies were hopeful that a sympathetic ruler might attain the throne.