The Jesuits did not arrive in an empty field. In 595, St Carthage—Mochuda, the future founder of Lismore—is said to have established a monastery here with 800 monks before relocating south. The site was already sacred ground when the Jesuits returned to Ireland after the dissolution of their order and accepted the lands at Tullabeg in 1818, leased permanently to Charles Aylmer by Maria O'Brien of the local gentry. The Presentation Sisters established a convent in Killina at the same time. The Jesuits founded their college as a feeder school for boys under thirteen, intended to prepare upper-middle-class Catholics to graduate on to Clongowes Wood College in Kildare. The school was endowed by the O'Briens, who had built their fortunes during the Catholic recovery of the eighteenth century.

Under William Delany's rectorship from 1870 to 1880, Tullabeg developed an unusual academic ambition. Like Carlow College and St Patrick's College, Thurles, it had its students matriculated and examined externally by the University of London for BA degrees—a workaround for Catholics who were largely excluded from Trinity College Dublin and unable to attend Catholic universities recognised by the state. When the Royal University of Ireland was established in 1882, Tullabeg pupils began progressing to the Jesuit University College Dublin, where they consistently achieved high marks in Royal University examinations. Water polo was played at the school, with the first pitch laid under Delany's rectorship and facilities developed by Karl Wisthoff, a German Jesuit. In 1886 the school was closed and the boys were transferred to Clongowes, possibly because of a shortage of priests.

From 1888, Tullabeg became a novitiate for Jesuit recruits—the place where men in their late teens or early twenties began the long formation that could last fifteen years. In 1918 it was formalised as a House of Probation and Studies. Among the novices who spent time at Tullabeg was Francis Browne, who entered in 1897 and spent two years there before being ordained. Browne is now best remembered for one thing: in April 1912, on a brief leg of the Titanic's maiden voyage from Southampton to Queenstown (Cobh), he took the only known photographs of life aboard the ship. He disembarked at Queenstown. The ship sailed on without him. The photographs are among the most famous historical images ever made, and the photographer was a Tullabeg Jesuit who survived because his order called him back to formation.

Gerard Manley Hopkins—the great Victorian Jesuit poet, then Professor of Classics at University College Dublin—came to Tullabeg in his final year, 1888–1889, for what would be his last retreat. His notes from those days are some of the bleakest writing in nineteenth-century English-language spiritual literature. He recorded a sense of futility, of being 'time's eunuch,' of failing both his vocation and his vocation's God. Hopkins died of typhoid the following June at age 44, his poetry mostly unpublished. The retreat notes from Tullabeg survived, copied by his Jesuit superiors and eventually published with his collected works. The Bog was the last place he wrote his despair down.

The chapel at Tullabeg held seven stained-glass windows by Evie Hone, one of the great Irish modernist artists of the twentieth century, commissioned by rector Donal O'Sullivan in the 1940s. The altar was designed by the architect Michael Scott with an altar front carved by Laurence Campbell. When the philosophy school relocated to Milltown Park in Dublin in 1962 and the retreat house finally closed after Easter 1991, Brendan Murray serving as last rector, the Hone windows were carefully removed and installed at the Jesuit Residence at Manresa House, Dublin, where they remain. The altar went to the Catholic church in Mucklagh. The buildings became a nursing home, then a golf club with a 9-hole course, then a property under administration that was vandalised when a security company failed to protect it—lead stripped from the roof, fittings stolen. As of recent surveys the main building is boarded up. The Jesuit cemetery beside the rear avenue still holds 42 Jesuits and one lay college worker, headstones now displaced and burial locations no longer reliable. The Bog has gone quiet. The men who shaped it are buried in it.