The archaeologist Christiaan Corlett, surveying the prehistoric monuments that ring the Reek, concluded that the mountain has been a local spiritual inspiration since at least the Neolithic. By the Bronze Age it had become the focus of an extensive ritual landscape. A short walk east of the summit lies the Boheh Stone, an outcrop covered with more than 260 rock carvings, one of the most detailed pieces of ancient rock art in Ireland. In 1987, observers noticed something extraordinary: from the Boheh Stone in late April and late August, the setting sun appears to roll down the slope of Croagh Patrick. It is believed the stone was placed precisely to mark this alignment. A stone row at Killadangan further marks the niche where the sun sets on the winter solstice.

In the 7th century, the Connacht writer Tirechan recorded that Saint Patrick spent forty days on the mountain. The 9th-century Bethu Phadraic adds that demons in the form of black birds harassed Patrick at the summit until he banished them into a hollow called Lugnademon, the hollow of the demons, by ringing his bell. According to the tradition, Patrick broke his fast only when God granted him the right to judge all the Irish at the Last Judgement and agreed to spare the land from final desolation. Another legend tells of a demonic female serpent named Corra whom Patrick banished into Lough Na Corra below the mountain, the lake bursting forth from the hollow she created in her fall.

The folklorist Maire MacNeill argued that the pilgrimage predates Christianity entirely. In her view, the climb was originally a ritual of Lughnasadh, the Celtic harvest festival. Christianity absorbed and renamed it. Today the climb takes place on the last Sunday of July, and Mass is held at the small summit chapel, which was dedicated on 20 July 1905. Some pilgrims climb barefoot as an act of penance, walking on quartzite scree that cuts and bruises the soles. Others perform rounding rituals, walking sunwise around ancient cairns called Reilig Mhuire, Mary's graveyard, which archaeologists believe are Bronze Age burial mounds. Until 1970 it was traditional to climb at night, possibly a survival of the older practice of summiting after viewing the rolling sun phenomenon at the Boheh Stone.

Forty thousand pilgrims a year, climbing a single steep slope of loose quartzite, leaves a mark. By the 2010s the mountain was suffering severe erosion that made the climb increasingly dangerous. Local stakeholders responded by building a stone path up the mountain, composed of stone from Croagh Patrick itself and laid in the dry-stone manner of traditional Irish walls. The work, more than three years in the making, neared completion in 2024. The path is a compromise between preserving the mountain and preserving the pilgrimage, and it represents an old Irish negotiation: how to honour what was while protecting what is left.

In the 1980s a seam of gold was discovered in the core of the Reek. The discovery could have been transformative for the local economy, and applications for mining licences followed. But the Mayo Environmental Group, headed by Paddy Hopkins, organised resistance, and Mayo County Council ultimately decided that no mining would be permitted on the holy mountain. The decision was unusual in Irish economic history and revealing of how the mountain is regarded locally. Even the name of the Owenwee River on the south slope, the yellow river in Irish, may preserve an ancient awareness of the gold below. The river still runs, the gold remains in the quartzite, and the pilgrims still climb.